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Complete Course of Mathematics
Topic 1: Numbers & Numerical Applications Topic 2: Algebra Topic 3: Quantitative Aptitude
Topic 4: Geometry Topic 5: Construction Topic 6: Coordinate Geometry
Topic 7: Mensuration Topic 8: Trigonometry Topic 9: Sets, Relations & Functions
Topic 10: Calculus Topic 11: Mathematical Reasoning Topic 12: Vectors & Three-Dimensional Geometry
Topic 13: Linear Programming Topic 14: Index Numbers & Time-Based Data Topic 15: Financial Mathematics
Topic 16: Statistics & Probability


Content On This Page
Fundamental Operations (Addition, Subtraction, Multiplication, Division) on Whole Numbers Operations on Integers Operations on Fractions
Operations on Decimal Numbers Operations on Rational Numbers Operations on Real Numbers
Order of Operations (BODMAS/PEMDAS) Simplification of Expressions involving various Number Types


Arithmetic Operations on Numbers



Fundamental Operations (Addition, Subtraction, Multiplication, Division) on Whole Numbers

Arithmetic operations are the core of numerical computations. They are the procedures used to combine numbers to produce a new value. The four fundamental arithmetic operations are Addition, Subtraction, Multiplication, and Division. We begin our study of these operations with the set of Whole Numbers ($\mathbb{W} = \{0, 1, 2, 3, ...\}$), which includes zero and the natural numbers.

Understanding how these operations behave within the set of whole numbers lays the groundwork for working with larger sets of numbers.


1. Addition (+) on Whole Numbers

Addition is the process of combining two or more numbers to find their total, called the sum. It can be visualized as bringing collections of objects together or moving to the right on the number line.

Properties of Addition on Whole Numbers: Let $a, b,$ and $c$ be any whole numbers.

Performing Addition: Addition of larger numbers is typically performed using column addition, aligning digits by their place value.

Example 1. Find the sum of $125$ and $248$.

Answer:

We align the numbers vertically by place value (Ones under Ones, Tens under Tens, etc.) and add column by column, starting from the rightmost column (Ones place). We carry over any sum of 10 or more to the next column to the left.

$$ \begin{array}{cccc} & 1 & 2 & 5 \\ + & 2 & 4 & 8 \\ \hline & 3 & 7 & 3 \\ \hline \end{array} $$

Step 1 (Ones place): Add the digits in the Ones column: $5 + 8 = 13$. Write down $3$ in the Ones place of the sum and carry over $1$ to the Tens place.

Step 2 (Tens place): Add the digits in the Tens column plus the carry-over: $1$ (carry) $+ 2 + 4 = 7$. Write down $7$ in the Tens place of the sum.

Step 3 (Hundreds place): Add the digits in the Hundreds column: $1 + 2 = 3$. Write down $3$ in the Hundreds place of the sum.

The sum of $125$ and $248$ is $\mathbf{373}$.


2. Subtraction (-) on Whole Numbers

Subtraction is the inverse operation of addition. It is used to find the difference between two numbers or to determine how much remains when a quantity is taken away from another. For whole numbers, subtraction is only defined when the number being subtracted (the subtrahend) is less than or equal to the number from which it is being subtracted (the minuend).

Properties of Subtraction on Whole Numbers: Let $a$ and $b$ be whole numbers.

Performing Subtraction: Subtraction of larger numbers is typically performed using column subtraction, aligning digits by place value and using borrowing (or regrouping) when a digit is smaller than the digit below it.

Example 1. Subtract $38$ from $95$.

Answer:

We write the larger number (minuend) above the smaller number (subtrahend), aligning the digits by place value. We subtract column by column, starting from the right.

$$ \begin{array}{cc} & \overset{8}{\cancel{9}} & \overset{15}{\cancel{5}} \\ - & 3 & 8 \\ \hline & 5 & 7 \\ \hline \end{array} $$

Step 1 (Ones place): Subtract the digits in the Ones column: $5 - 8$. Since $5$ is less than $8$, we need to borrow from the Tens place. Borrow $1$ Ten (which is 10 Ones) from the 9 Tens in the Tens place. The 9 Tens become 8 Tens, and the 5 Ones become $5 + 10 = 15$ Ones. Now subtract: $15 - 8 = 7$. Write down $7$ in the Ones place of the difference.

Step 2 (Tens place): Subtract the digits in the Tens column. The original 9 Tens are now 8 Tens (after borrowing). Subtract the subtrahend's Tens digit: $8 - 3 = 5$. Write down $5$ in the Tens place of the difference.

The difference is $\mathbf{57}$.


3. Multiplication ($\times$ or $\cdot$) on Whole Numbers

Multiplication is often introduced as repeated addition. For example, $3 \times 4$ means adding 3 to itself 4 times ($3 + 3 + 3 + 3 = 12$), or adding 4 to itself 3 times ($4 + 4 + 4 = 12$). The result of multiplication is called the product.

Properties of Multiplication on Whole Numbers: Let $a, b,$ and $c$ be any whole numbers.

Performing Multiplication: For multiplying numbers with more than one digit, long multiplication based on place value is used.

Example 1. Find the product of $45$ and $23$.

Answer:

We multiply 45 by the Ones digit of 23, then by the Tens digit of 23, and add the results (called partial products).

$$ \begin{array}{cc}& & 4 & 5 \\ \times & & 2 & 3 \\ \hline & 1 & 3 & 5 & \quad \leftarrow 45 \times 3 \\ 9 & 0 & \times & \quad \leftarrow 45 \times 20 \text{ (write 0 in ones place, then } 45 \times 2) \\ \hline 1 & 0 & 3 & 5 \\ \hline \end{array} $$

Step 1: Multiply 45 by the Ones digit (3): $45 \times 3$.

$3 \times 5 = 15$. Write 5, carry 1.

$3 \times 4 = 12$. Add the carry-over: $12 + 1 = 13$. Write 13.

Partial product 1: 135.

Step 2: Multiply 45 by the Tens digit (2, which represents 20): $45 \times 20$. Write a 0 in the Ones place of the second partial product to account for multiplying by 20. Then multiply 45 by 2.

$2 \times 5 = 10$. Write 0 (next to the initial 0), carry 1.

$2 \times 4 = 8$. Add the carry-over: $8 + 1 = 9$. Write 9.

Partial product 2: 900.

Step 3: Add the partial products: $135 + 900$.

$$ \begin{array}{cccc} & 1 & 3 & 5 \\ + & 9 & 0 & 0 \\ \hline 1 & 0 & 3 & 5 \\ \hline \end{array} $$

The product of $45$ and $23$ is $\mathbf{1035}$.


4. Division ($\div$ or /) on Whole Numbers

Division is the inverse operation of multiplication. It is used to share a quantity into equal parts (partitioning) or to find out how many times one quantity is contained within another (quotitioning). For example, $12 \div 4$ can mean sharing 12 into 4 equal groups (each has 3) or finding how many groups of 4 are in 12 (there are 3 groups).

Rules: Division of whole numbers is not closed, not commutative, and not associative. Division by zero is undefined.

When a whole number $a$ is divided by a non-zero whole number $b$, we use the division algorithm, which states that there exist unique whole numbers, a quotient $q$ and a remainder $r$, such that:

$\quad a = b \times q + r$, where $0 \le r < b$

[Division Algorithm]

If the remainder $r$ is $0$, the division is exact, and $b$ is a factor of $a$. The quotient $q = a \div b$.

Performing Division: For dividing larger numbers, long division is a standard method.

Example 1. Divide $125$ by $5$. Find the quotient and remainder.

Answer:

We use the long division process:

$$ \begin{array}{r} 25 \phantom{)} \leftarrow \text{Quotient} \\ \text{Divisor } 5{\overline{\smash{\big)}\,125\phantom{)}} \leftarrow \text{Dividend}} \\ \underline{-~\phantom{(}10\phantom{0)}} \\ 25\phantom{)} \\ \underline{-~\phantom{(}25\phantom{)}} \\ 0\phantom{)} \leftarrow \text{Remainder} \end{array} $$

Step 1: Start with the leftmost digit(s) of the dividend (125) that are greater than or equal to the divisor (5). Here, $1 < 5$, so take the first two digits, 12.

Divide 12 by 5. The largest multiple of 5 that is less than or equal to 12 is 10 ($5 \times 2$). Write the quotient digit 2 above the 2 in 125.

Multiply the quotient digit (2) by the divisor (5): $2 \times 5 = 10$. Write 10 below 12.

Subtract 10 from 12: $12 - 10 = 2$.

Step 2: Bring down the next digit of the dividend (5) next to the remainder 2. This forms the new number 25.

Step 3: Divide 25 by 5. The largest multiple of 5 that is less than or equal to 25 is 25 ($5 \times 5$). Write the quotient digit 5 above the 5 in 125.

Multiply the quotient digit (5) by the divisor (5): $5 \times 5 = 25$. Write 25 below 25.

Subtract 25 from 25: $25 - 25 = 0$.

Since the remainder is 0 and there are no more digits to bring down, the division is complete.

The quotient is $\mathbf{25}$ and the remainder is $\mathbf{0}$. This means $125 = 5 \times 25 + 0$.


Example 2. Divide $137$ by $8$. Find the quotient and remainder.

Answer:

We use long division:

$$ \begin{array}{r} 17 \phantom{)} \\ 8{\overline{\smash{\big)}\,137\phantom{)}}} \\ \underline{-~\phantom{(}8\phantom{0)}} \\ 57\phantom{)} \\ \underline{-~\phantom{(}56\phantom{)}} \\ 1\phantom{)} \end{array} $$

Step 1: Divide 13 (first two digits of 137) by 8. Largest multiple of 8 less than or equal to 13 is 8 ($8 \times 1$). Write 1 in the quotient above the 3 in 137. Multiply $1 \times 8 = 8$. Subtract $13 - 8 = 5$.

Step 2: Bring down the next digit (7) to form 57.

Step 3: Divide 57 by 8. Largest multiple of 8 less than or equal to 57 is 56 ($8 \times 7$). Write 7 in the quotient above the 7 in 137. Multiply $7 \times 8 = 56$. Subtract $57 - 56 = 1$.

The remainder is 1, which is less than the divisor 8. No more digits to bring down.

The quotient is $\mathbf{17}$ and the remainder is $\mathbf{1}$. This means $137 = 8 \times 17 + 1$.



Operations on Integers

The set of Integers ($\mathbb{Z} = \{..., -3, -2, -1, 0, 1, 2, 3, ...\}$) includes all whole numbers and their negative counterparts. When performing arithmetic operations on integers, we need to consider the sign of each number, as the rules for operations involving positive and negative numbers differ from operations solely involving whole numbers.


1. Addition (+) of Integers

Adding integers depends on whether the numbers have the same sign or different signs.

Properties of Addition on Integers: Addition of integers satisfies the same properties as for whole numbers, plus the existence of additive inverses:

Visualizing Addition on Number Line: Starting from the position of the first number, move to the right for adding a positive number, and move to the left for adding a negative number. The distance moved is equal to the absolute value of the second number.

Number line showing 3 + (-5) = -2

(Note: The image shows a number line. An arrow starts at 0 and goes to 3 (representing the first number). From 3, another arrow points left 5 units (representing adding -5). The second arrow ends at -2, showing that $3 + (-5) = -2$.)


2. Subtraction (-) of Integers

Subtraction of integers is defined as adding the additive inverse (opposite) of the number being subtracted.

For any integers $a, b$, $\quad a - b = a + (-b)$

[Rule for Integer Subtraction]

To subtract an integer $b$ from an integer $a$, change the sign of $b$ to its opposite (its additive inverse, $-b$), and then add $a$ and $-b$ following the rules for integer addition.

Examples:

Properties of Subtraction on Integers:

Visualizing Subtraction on Number Line: Using the rule $a - b = a + (-b)$, subtraction is visualized as addition of the inverse. Starting from the position of the first number, move to the left for subtracting a positive number (adding a negative), and move to the right for subtracting a negative number (adding a positive). The distance moved is the absolute value of the number being subtracted.

Number line showing 3 - (-5) = 8

(Note: The image shows a number line. An arrow starts at 0 and goes to 3. From 3, an arrow points right 5 units (representing subtracting -5, which is adding 5). The second arrow ends at 8, showing that $3 - (-5) = 3 + 5 = 8$).


3. Multiplication ($\times$ or $\cdot$) of Integers

Multiplying integers involves considering the signs of the numbers being multiplied. The rule for determining the sign of the product is critical.

Rules for Signs in Multiplication: For any positive integers $a$ and $b$:

Summary of Sign Rules:

The magnitude of the product is found by multiplying the absolute values of the two integers: $|a \times b| = |a| \times |b|$.

Properties of Multiplication on Integers: Multiplication of integers shares the same properties as for whole numbers:


4. Division ($\div$ or /) of Integers

Division is the inverse operation of multiplication. For any integers $a$ and $b$ (with $b \neq 0$), $a \div b = q$ if and only if $a = b \times q$. The result of division is called the quotient.

The rules for the sign of the quotient are the same as the rules for the sign of the product (when the divisor is non-zero).

Rules for Signs in Division: For any integers $a$ and $b$, with $b \neq 0$:

Summary of Sign Rules:

The magnitude of the quotient is found by dividing the absolute values: $|\frac{a}{b}| = \frac{|a|}{|b|}$.

Division by Zero: As with whole numbers, division by zero is undefined for integers.

Properties of Division on Integers:

When integer division is not exact (i.e., the remainder is not 0), the result is not an integer. In such cases, the result is expressed as a rational number (a fraction) or a decimal.


Summary of Operations on Integers

Operation Sign Rules Properties Visualisation (Number Line)
Addition (+) Same signs: Add absolute values, keep sign.
Different signs: Subtract smaller absolute value from larger, keep sign of number with larger absolute value.
Closed, Commutative, Associative, Identity (0), Inverse (for all $a$, $-a$). Start at first number. Move right for positive, left for negative. Distance is absolute value.
Subtraction (-) $a - b = a + (-b)$. Apply addition rules. Closed, Not Commutative, Not Associative. Start at first number. Move left for positive $b$, right for negative $b$. Distance is absolute value of $b$.
Multiplication ($\times$) Same signs: Positive product.
Different signs: Negative product.
Closed, Commutative, Associative, Identity (1), Property of Zero (result 0). Distributive. Can be visualized as repeated addition/subtraction from 0. e.g., $3 \times (-2)$ is 3 steps of -2 from 0.
Division ($\div$) Same signs: Positive quotient.
Different signs: Negative quotient. (For $b \neq 0$)
Not Closed, Not Commutative, Not Associative. Division by zero undefined. Can be visualized as finding how many steps of the divisor are needed to reach the dividend from 0.

Mastering these rules and properties is fundamental for working with rational and real numbers, as they build upon the operations defined for integers.



Operations on Fractions

Fractions are numbers that can be expressed in the form $\frac{p}{q}$, where $p$ and $q$ are integers and $q$ is a non-zero integer ($q \neq 0$). Performing the fundamental arithmetic operations (addition, subtraction, multiplication, and division) with fractions requires specific rules that involve their numerators and denominators.

Let $\frac{a}{b}$ and $\frac{c}{d}$ be two fractions, where $a, b, c, d \in \mathbb{Z}$ and $b \neq 0, d \neq 0$.


1. Addition (+) of Fractions

Adding fractions depends on whether they have the same denominator or different denominators.

Adding Mixed Numbers: To add mixed numbers, convert them into improper fractions first, and then add the improper fractions using the rules above. Alternatively, you can add the whole number parts and the fractional parts separately, regrouping if the sum of the fractional parts is an improper fraction.

Example: Add $2\frac{1}{2}$ and $1\frac{3}{4}$.

Method 1 (Improper Fractions): Convert to improper fractions: $2\frac{1}{2} = \frac{(2 \times 2) + 1}{2} = \frac{5}{2}$. $1\frac{3}{4} = \frac{(1 \times 4) + 3}{4} = \frac{7}{4}$.

Find LCM of denominators (2 and 4): LCM$(2, 4) = 4$. Convert $\frac{5}{2}$ to fourths: $\frac{5 \times 2}{2 \times 2} = \frac{10}{4}$.

Add: $\frac{10}{4} + \frac{7}{4} = \frac{10+7}{4} = \frac{17}{4}$. Convert back to mixed number: $\frac{17}{4} = 4$ with remainder 1, so $4\frac{1}{4}$.

Method 2 (Separate Parts): Add whole numbers: $2+1=3$. Add fractions: $\frac{1}{2} + \frac{3}{4} = \frac{2}{4} + \frac{3}{4} = \frac{5}{4}$. Convert improper fraction sum to mixed: $\frac{5}{4} = 1\frac{1}{4}$. Add the whole number sum and the mixed fraction sum: $3 + 1\frac{1}{4} = 4\frac{1}{4}$.


2. Subtraction (-) of Fractions

Subtracting fractions follows similar steps to adding fractions, especially regarding common denominators.

Subtracting Mixed Numbers: Convert mixed numbers to improper fractions first, then subtract. Or, subtract whole numbers and fractional parts separately, borrowing from the whole number part if the first fraction is smaller than the second fraction.

Example: Subtract $1\frac{3}{4}$ from $2\frac{1}{2}$.

Method 1 (Improper Fractions): Convert to improper fractions: $2\frac{1}{2} = \frac{5}{2}$, $1\frac{3}{4} = \frac{7}{4}$.

Find LCM of denominators (2 and 4): LCM$(2, 4) = 4$. Convert $\frac{5}{2}$ to fourths: $\frac{5 \times 2}{2 \times 2} = \frac{10}{4}$.

Subtract: $\frac{10}{4} - \frac{7}{4} = \frac{10-7}{4} = \frac{3}{4}$.

Method 2 (Separate Parts with Borrowing): $2\frac{1}{2} - 1\frac{3}{4}$. We can't subtract $\frac{3}{4}$ from $\frac{1}{2}$. Borrow 1 whole from 2: $2\frac{1}{2} = 1 + 1\frac{1}{2} = 1 + \frac{3}{2} = 1 + \frac{6}{4}$. So $2\frac{1}{2} = 1\frac{6}{4}$.

Now subtract: $1\frac{6}{4} - 1\frac{3}{4}$. Subtract whole numbers: $1-1=0$. Subtract fractions: $\frac{6}{4} - \frac{3}{4} = \frac{6-3}{4} = \frac{3}{4}$. Result: $0 + \frac{3}{4} = \frac{3}{4}$.


3. Multiplication ($\times$ or $\cdot$) of Fractions

Multiplying fractions is generally simpler than adding or subtracting them because it does not require finding a common denominator.

Rule: To multiply two fractions, multiply the numerators together to get the new numerator, and multiply the denominators together to get the new denominator.

$\quad \frac{a}{b} \times \frac{c}{d} = \frac{a \times c}{b \times d} \quad (\text{where } b \neq 0, d \neq 0)$

It is often beneficial to simplify the fractions before multiplying by canceling out any common factors between any numerator and any denominator (known as cross-cancellation).

Examples:

Example 1. Multiply $\frac{2}{3} \times \frac{5}{7}$.

Answer:

Multiply the numerators ($2 \times 5$) and the denominators ($3 \times 7$).

$\quad \frac{2}{3} \times \frac{5}{7} = \frac{2 \times 5}{3 \times 7} = \frac{10}{21}$


Example 2. Multiply $\frac{3}{4} \times \frac{8}{9}$.

Answer:

We can simplify by canceling common factors before multiplying:

  • 3 in the numerator of the first fraction and 9 in the denominator of the second fraction share a common factor of 3. Divide both by 3.
  • 4 in the denominator of the first fraction and 8 in the numerator of the second fraction share a common factor of 4. Divide both by 4.

$\quad \frac{\cancel{3}^{1}}{\cancel{4}_{1}} \times \frac{\cancel{8}^{2}}{\cancel{9}_{3}}$

Now multiply the simplified fractions:

$\quad = \frac{1}{1} \times \frac{2}{3} = \frac{1 \times 2}{1 \times 3} = \frac{2}{3}$

Alternatively, multiply directly and then simplify the result:

$\quad \frac{3}{4} \times \frac{8}{9} = \frac{3 \times 8}{4 \times 9} = \frac{24}{36}$

Simplify $\frac{24}{36}$ by dividing the numerator and denominator by their greatest common divisor, which is 12:

$\quad \frac{\cancel{24}^{2}}{\cancel{36}_{3}} = \frac{2}{3}$

Both methods yield the same result.

Multiplying Mixed Numbers: Always convert mixed numbers to improper fractions before multiplying. Then, multiply the improper fractions using the rule.

Example: Multiply $1\frac{1}{2}$ by $2\frac{1}{3}$.

Convert to improper fractions: $1\frac{1}{2} = \frac{(1 \times 2) + 1}{2} = \frac{3}{2}$. $2\frac{1}{3} = \frac{(2 \times 3) + 1}{3} = \frac{7}{3}$.

Multiply the improper fractions: $\frac{3}{2} \times \frac{7}{3}$. Cancel the common factor 3:

$\quad \frac{\cancel{3}^{1}}{2} \times \frac{7}{\cancel{3}_{1}} = \frac{1 \times 7}{2 \times 1} = \frac{7}{2}$

The result $\frac{7}{2}$ can be left as an improper fraction or converted to a mixed number: $3\frac{1}{2}$.


4. Division ($\div$ or /) of Fractions

Dividing by a fraction is equivalent to multiplying the first fraction by the reciprocal of the second fraction (the divisor).

The reciprocal of a non-zero fraction $\frac{c}{d}$ is obtained by swapping its numerator and denominator, resulting in $\frac{d}{c}$. Note that the original fraction must be non-zero for its reciprocal to exist (i.e., $c \neq 0$).

Rule: To divide a fraction $\frac{a}{b}$ by a non-zero fraction $\frac{c}{d}$, multiply $\frac{a}{b}$ by the reciprocal of $\frac{c}{d}$.

$\quad \frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c} \quad (\text{where } b \neq 0, c \neq 0, d \neq 0)$

Examples:

Example 1. Divide $\frac{2}{3}$ by $\frac{1}{4}$.

Answer:

The reciprocal of the divisor $\frac{1}{4}$ is $\frac{4}{1}$. Multiply $\frac{2}{3}$ by $\frac{4}{1}$.

$\quad \frac{2}{3} \div \frac{1}{4} = \frac{2}{3} \times \frac{4}{1} = \frac{2 \times 4}{3 \times 1} = \frac{8}{3}$


Example 2. Divide $5$ by $\frac{2}{3}$.

Answer:

First, write the whole number 5 as a fraction: $\frac{5}{1}$. The reciprocal of the divisor $\frac{2}{3}$ is $\frac{3}{2}$.

Multiply $\frac{5}{1}$ by $\frac{3}{2}$.

$\quad 5 \div \frac{2}{3} = \frac{5}{1} \div \frac{2}{3} = \frac{5}{1} \times \frac{3}{2} = \frac{5 \times 3}{1 \times 2} = \frac{15}{2}$

The result $\frac{15}{2}$ can be converted to a mixed number: $7\frac{1}{2}$.

Dividing Mixed Numbers: Always convert mixed numbers to improper fractions before dividing. Then, divide the improper fractions using the rule (multiply by the reciprocal of the divisor).

Example: Divide $3\frac{1}{2}$ by $1\frac{1}{4}$.

Convert to improper fractions: $3\frac{1}{2} = \frac{(3 \times 2) + 1}{2} = \frac{7}{2}$. $1\frac{1}{4} = \frac{(1 \times 4) + 1}{4} = \frac{5}{4}$.

Divide the improper fractions: $\frac{7}{2} \div \frac{5}{4}$. The reciprocal of $\frac{5}{4}$ is $\frac{4}{5}$.

Multiply: $\frac{7}{2} \times \frac{4}{5}$. Cancel the common factor 2:

$\quad \frac{7}{\cancel{2}_{1}} \times \frac{\cancel{4}^{2}}{5} = \frac{7 \times 2}{1 \times 5} = \frac{14}{5}$

The result $\frac{14}{5}$ can be converted to a mixed number: $2\frac{4}{5}$.


Summary of Operations on Fractions

Operation Rule Notes
Addition (+) Common Denominator: $\frac{a}{d} + \frac{b}{d} = \frac{a+b}{d}$
Different Denominators: Convert to common denominator (LCM), then add numerators.
LCM is preferred for efficiency.
Convert mixed numbers to improper fractions first.
Subtraction (-) Common Denominator: $\frac{a}{d} - \frac{b}{d} = \frac{a-b}{d}$
Different Denominators: Convert to common denominator (LCM), then subtract numerators.
LCM is preferred for efficiency.
Convert mixed numbers to improper fractions first.
Subtracting a negative fraction is adding a positive fraction.
Multiplication ($\times$) $\frac{a}{b} \times \frac{c}{d} = \frac{a \times c}{b \times d}$ Multiply numerators, multiply denominators.
Simplify by cross-cancellation before multiplying is often easier.
Convert mixed numbers to improper fractions first.
Division ($\div$) $\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c}$ (Multiply by the reciprocal of the divisor, $c \neq 0$) Reciprocal of $\frac{c}{d}$ is $\frac{d}{c}$.
Division by zero is undefined.
Convert mixed numbers to improper fractions first.

These rules allow us to perform all four basic arithmetic operations within the set of rational numbers (since integers and fractions cover all rational numbers), maintaining closure under addition, subtraction, and multiplication, and closure under division by any non-zero rational number.



Operations on Decimal Numbers

Decimal numbers are a convenient way to represent numbers, particularly rational numbers whose denominator is a power of 10. Operations on decimals are extensions of operations on whole numbers, requiring careful handling of the decimal point based on its place value significance.


1. Addition (+) of Decimal Numbers

To add decimal numbers, the key is to ensure that digits of the same place value are added together. This is achieved by aligning the decimal points vertically.

Steps for Adding Decimals:

  1. Write the numbers vertically, aligning the decimal points.
  2. Add trailing zeros to the end of any number(s) so that all numbers have the same number of decimal places. This helps align the place values visually, but is not strictly necessary mathematically.
  3. Add the numbers column by column from right to left, just as you would with whole numbers. Carry over digits when a sum in a column is 10 or greater.
  4. Place the decimal point in the sum directly below the aligned decimal points in the numbers being added.

Example:

Example 1. Add $12.35$ and $4.8$.

Answer:

Write the numbers vertically, aligning the decimal points. Add a trailing zero to $4.8$ to make it $4.80$ for easier alignment of hundredths place.

$$ \begin{array}{cc} & 12.35 \\ + & \phantom{0}4.80 \\ \hline & 17.15 \\ \hline \end{array} $$

Step 1 (Hundredths place): $5 + 0 = 5$. Write $5$ in the hundredths place of the sum.

Step 2 (Tenths place): $3 + 8 = 11$. Write $1$ in the tenths place of the sum and carry over $1$ to the Ones place.

Step 3 (Decimal Point): Place the decimal point in the sum directly below the decimal points above it.

Step 4 (Ones place): Add the digits in the Ones column plus the carry-over: $1$ (carry) $+ 2 + 4 = 7$. Write $7$ in the Ones place of the sum.

Step 5 (Tens place): Add the digits in the Tens column: $1 + 0 = 1$. Write $1$ in the Tens place of the sum.

The sum of $12.35$ and $4.8$ is $\mathbf{17.15}$.


2. Subtraction (-) of Decimal Numbers

Subtracting decimal numbers also requires aligning the decimal points to ensure subtraction of digits from corresponding place values.

Steps for Subtracting Decimals:

  1. Write the numbers vertically, aligning the decimal points. Place the number being subtracted (subtrahend) below the number it is being subtracted from (minuend).
  2. Add trailing zeros to the minuend so that it has at least as many decimal places as the subtrahend. This is essential for correct borrowing.
  3. Subtract the numbers column by column from right to left, just as you would with whole numbers. Use borrowing (regrouping) when a digit in the minuend is smaller than the corresponding digit in the subtrahend.
  4. Place the decimal point in the difference directly below the aligned decimal points.

Example:

Example 1. Subtract $6.75$ from $10.2$.

Answer:

Write the numbers vertically, aligning decimal points. The number being subtracted is 6.75. The number it is subtracted from is 10.2.

Add a trailing zero to 10.2 to make it 10.20.

$$ \begin{array}{cc} & \overset{9}{\cancel{10}}.\overset{11}{\cancel{2}}\overset{10}{0} \\ - & \phantom{0}6.75 \\ \hline & \phantom{0}3.45 \\ \hline \end{array} $$

Step 1 (Hundredths place): Subtract digits in the hundredths column: $0 - 5$. We need to borrow. Borrow $1$ tenth from the Tenths place of 10.20 (leaving 1 tenth). Add 10 hundredths to the 0 hundredths: $0 + 10 = 10$. Now subtract: $10 - 5 = 5$. Write $5$ in the hundredths place of the difference.

Step 2 (Tenths place): Subtract digits in the tenths column. We now have 1 in the tenths place (after borrowing). $1 - 7$. We need to borrow from the Ones place. Borrow 1 One from the Ones place of 10 (leaving 9 ones). Add 10 tenths to the 1 tenth: $1 + 10 = 11$ tenths. Now subtract: $11 - 7 = 4$. Write $4$ in the tenths place of the difference.

Step 3 (Decimal Point): Place the decimal point in the difference.

Step 4 (Ones place): Subtract digits in the Ones column. We now have 9 in the Ones place (after borrowing from 10). $9 - 6 = 3$. Write $3$ in the Ones place of the difference.

Step 5 (Tens place): Subtract digits in the Tens column: $0 - 0 = 0$. (The 1 from 10 was borrowed, leaving 0 in the tens place of 10).

The difference is $\mathbf{3.45}$.


3. Multiplication ($\times$ or $\cdot$) of Decimal Numbers

Multiplying decimal numbers involves two main steps: performing the multiplication as if they were whole numbers and then correctly placing the decimal point in the product.

Steps for Multiplying Decimals:

  1. Multiply the numbers as if they were whole numbers, ignoring the decimal points for the moment.
  2. Count the total number of decimal places in both of the original numbers being multiplied. This is the sum of the number of digits to the right of the decimal point in each factor.
  3. Place the decimal point in the product obtained in Step 1 such that there are exactly that many decimal places (the total count from Step 2), counting from the rightmost digit of the product. Add leading zeros if necessary to place the decimal point correctly.

Example:

Example 1. Multiply $2.5 \times 1.3$.

Answer:

Multiply 25 by 13 as if they were whole numbers:

$$ \begin{array}{cc} & 25 \\ \times & 13 \\ \hline & 75 & \leftarrow 25 \times 3 \\ 25 \times & \\ \hline 325 \\ \hline \end{array} $$

Count the total number of decimal places in the original numbers:

Number $2.5$ has 1 decimal place (the digit 5).

Number $1.3$ has 1 decimal place (the digit 3).

Total number of decimal places in the factors $= 1 + 1 = 2$.

Starting from the rightmost digit of the product (325), count 2 places to the left and place the decimal point.

The product is $\mathbf{3.25}$.


Example 2. Multiply $0.06 \times 0.4$.

Answer:

Multiply 6 by 4 as whole numbers:

$\quad 6 \times 4 = 24$

Count the total number of decimal places in the original numbers:

Number $0.06$ has 2 decimal places (0 and 6).

Number $0.4$ has 1 decimal place (4).

Total number of decimal places in the factors $= 2 + 1 = 3$.

The product of 6 and 4 is 24. We need to place the decimal point so there are 3 decimal places. Starting from the right of 24, count 3 places to the left. We need to add a leading zero.

The digits are $024$. Placing the decimal point 3 places from the right gives $0.024$.

The product is $\mathbf{0.024}$.


4. Division ($\div$ or /) of Decimal Numbers

Dividing decimal numbers is often easiest when the divisor (the number you are dividing by) is a whole number. We can achieve this by multiplying both the divisor and the dividend (the number being divided) by the same power of 10. This does not change the value of the quotient.

Steps for Dividing Decimals:

  1. If the divisor is a decimal, move the decimal point in the divisor to the right until it becomes a whole number. Count the number of places moved.
  2. Move the decimal point in the dividend the same number of places to the right as you moved it in the divisor. Add trailing zeros to the dividend if necessary.
  3. Perform the division as if you are dividing a whole number by a whole number.
  4. Place the decimal point in the quotient directly above the new position of the decimal point in the dividend.
  5. Continue the division process until you get a remainder of zero or reach the desired number of decimal places in the quotient.

Example:

Example 1. Divide $14.4$ by $1.2$.

Answer:

The divisor is $1.2$. It has one decimal place. To make it a whole number, move the decimal point 1 place to the right ($1.2 \to 12$). Multiply the divisor by $10$.

Now, move the decimal point in the dividend $14.4$ the same number of places (1 place) to the right ($14.4 \to 144$). Multiply the dividend by $10$.

The problem becomes dividing $144$ by $12$.

$$ \begin{array}{r} 12 \leftarrow \text{Quotient} \\ 12{\overline{\smash{\big)}\,144}} \\ \underline{-~\phantom{(}12\phantom{0)}} \\ 24 \\ \underline{-~\phantom{(}24)} \\ 0 \leftarrow \text{Remainder} \end{array} $$

Divide 14 by 12 (1 time). $1 \times 12 = 12$. $14 - 12 = 2$. Bring down 4 to get 24.

Divide 24 by 12 (2 times). $2 \times 12 = 24$. $24 - 24 = 0$.

The quotient is 12. The decimal point in the quotient is placed directly above the decimal point in the modified dividend (144.), which is after the digit 2.

The result of $14.4 \div 1.2$ is $\mathbf{12}$.


Example 2. Divide $5.6$ by $0.07$.

Answer:

The divisor is $0.07$. It has two decimal places. To make it a whole number, move the decimal point 2 places to the right ($0.07 \to 7$). Multiply the divisor by $100$.

Move the decimal point in the dividend $5.6$ the same number of places (2 places) to the right ($5.6 \to 560$). We need to add one trailing zero.

The problem becomes dividing $560$ by $7$.

$$ \begin{array}{r} 80 \\ 7{\overline{\smash{\big)}\,560}} \\ \underline{-~\phantom{(}56\phantom{0)}} \\ 00 \\ \underline{-~\phantom{(}00)} \\ 0 \end{array} $$

Divide 56 by 7 (8 times). $8 \times 7 = 56$. $56 - 56 = 0$. Bring down 0.

Divide 0 by 7 (0 times). $0 \times 7 = 0$. $0 - 0 = 0$.

The quotient is 80. The decimal point is after the digit 0.

The result of $5.6 \div 0.07$ is $\mathbf{80}$.


Example 3. Divide $7$ by $0.2$.

Answer:

The divisor is $0.2$. Move the decimal point 1 place right ($0.2 \to 2$). Multiply by 10.

Move the decimal point in the dividend $7$ (which is $7.0$) 1 place right ($7.0 \to 70$). Multiply by 10.

The problem becomes dividing $70$ by $2$.

$$ \begin{array}{r} 35 \\ 2{\overline{\smash{\big)}\,70}} \\ \underline{-~\phantom{(}6\phantom{0)}} \\ 10 \\ \underline{-~\phantom{(}10)} \\ 0 \end{array} $$

Divide 7 by 2 (3 times). $3 \times 2 = 6$. $7 - 6 = 1$. Bring down 0 to get 10.

Divide 10 by 2 (5 times). $5 \times 2 = 10$. $10 - 10 = 0$.

The quotient is 35. The decimal point is after the digit 5.

The result of $7 \div 0.2$ is $\mathbf{35}$.



Operations on Rational Numbers

Rational numbers ($\mathbb{Q}$) encompass all numbers that can be expressed in the form $\frac{p}{q}$, where $p$ and $q$ are integers and $q \neq 0$. This includes integers, fractions, terminating decimals, and non-terminating repeating decimals. The arithmetic operations (addition, subtraction, multiplication, and division) can be performed on any pair of rational numbers by applying the rules for fractions or decimals.

The set of rational numbers, along with addition and multiplication, forms a mathematical structure known as a field, due to satisfying a specific set of properties.


Properties of Rational Numbers under Operations

Let $a, b,$ and $c$ be any three rational numbers.

These properties confirm that rational numbers behave consistently under the basic operations, forming a solid algebraic structure.


Examples of Operations on Rational Numbers

To perform operations on rational numbers given in different forms (fractions, decimals), you can either convert all numbers to fractions and apply fraction rules, or convert all numbers to decimals and apply decimal rules.

Example 1. Calculate $\frac{3}{5} + 0.75$.

Answer:

Method 1: Convert to Decimals

Convert the fraction $\frac{3}{5}$ to a decimal by dividing 3 by 5:

$\quad \frac{3}{5} = 3 \div 5 = 0.6$

Now add the two decimal numbers:

$\quad 0.6 + 0.75 = 1.35$

Method 2: Convert to Fractions

Convert the decimal $0.75$ to a fraction:

$\quad 0.75 = \frac{75}{100}$

Simplify the fraction:

$\quad \frac{\cancel{75}^{3}}{\cancel{100}_{4}} = \frac{3}{4}$

Now add the two fractions $\frac{3}{5}$ and $\frac{3}{4}$. Find a common denominator: LCM$(5, 4) = 20$.

$\quad \frac{3}{5} + \frac{3}{4} = \frac{3 \times 4}{5 \times 4} + \frac{3 \times 5}{4 \times 5} = \frac{12}{20} + \frac{15}{20} = \frac{12+15}{20} = \frac{27}{20}$

Both methods yield the same result. The result $\frac{27}{20}$ can be converted back to decimal form: $27 \div 20 = 1.35$.

The answer is $\mathbf{1.35}$ or $\mathbf{\frac{27}{20}}$.


Example 2. Calculate $2.5 \times (-\frac{1}{2})$.

Answer:

Method 1: Convert to Decimals

Convert the fraction $-\frac{1}{2}$ to a decimal:

$\quad -\frac{1}{2} = -0.5$

Now multiply the two decimal numbers:

$\quad 2.5 \times (-0.5)$

Multiply the absolute values: $2.5 \times 0.5 = 1.25$. Since we are multiplying a positive number by a negative number, the result is negative.

$\quad 2.5 \times (-0.5) = -1.25$

Method 2: Convert to Fractions

Convert the decimal $2.5$ to a fraction:

$\quad 2.5 = \frac{25}{10}$

Simplify the fraction:

$\quad \frac{\cancel{25}^{5}}{\cancel{10}_{2}} = \frac{5}{2}$

Now multiply the two fractions $\frac{5}{2}$ and $-\frac{1}{2}$. Multiply numerators and denominators, remembering the sign rules ($+ \times - = -$):

$\quad \frac{5}{2} \times (-\frac{1}{2}) = -\frac{5 \times 1}{2 \times 2} = -\frac{5}{4}$

Both methods give the same result. The result $-\frac{5}{4}$ can be converted back to decimal form: $-5 \div 4 = -1.25$.

The answer is $\mathbf{-1.25}$ or $\mathbf{-\frac{5}{4}}$.


Example 3. Calculate $0.8 \div \frac{4}{5}$.

Answer:

Method 1: Convert to Decimals

Convert the fraction $\frac{4}{5}$ to a decimal:

$\quad \frac{4}{5} = 4 \div 5 = 0.8$

Now divide the two decimal numbers:

$\quad 0.8 \div 0.8 = 1$

Method 2: Convert to Fractions

Convert the decimal $0.8$ to a fraction:

$\quad 0.8 = \frac{8}{10}$

Simplify the fraction:

$\quad \frac{\cancel{8}^{4}}{\cancel{10}_{5}} = \frac{4}{5}$

Now divide the two fractions $\frac{4}{5}$ by $\frac{4}{5}$. Dividing a non-zero number by itself gives 1.

$\quad \frac{4}{5} \div \frac{4}{5} = \frac{4}{5} \times \frac{5}{4} = \frac{\cancel{4}^1}{\cancel{5}_1} \times \frac{\cancel{5}^1}{\cancel{4}_1} = \frac{1 \times 1}{1 \times 1} = 1$

Both methods give the same result.

The answer is $\mathbf{1}$.



Operations on Real Numbers

The set of Real Numbers ($\mathbb{R}$) comprises both rational numbers ($\mathbb{Q}$) and irrational numbers ($\mathbb{I}$). Operations on real numbers build upon the rules for rational numbers and include methods for handling expressions involving irrational components. The set of real numbers, under the operations of addition and multiplication, forms a field, meaning it satisfies a comprehensive set of algebraic properties.


Properties of Real Numbers under Operations

For any real numbers $a, b,$ and $c$, the fundamental arithmetic operations satisfy the following properties:

These properties are the foundation for algebraic manipulations involving real numbers.


Operations Involving Irrational Numbers

While the properties hold for all real numbers, the result of operations specifically involving irrational numbers might be either rational or irrational. This was highlighted in the "Broad Classification of Numbers" section.

When performing operations, treat irrational parts (especially square roots) somewhat like variables in algebra. Combine 'like' irrational terms (those with the same radical part). Use properties like $\sqrt{a} \times \sqrt{b} = \sqrt{ab}$ (for $a, b \ge 0$), $(\sqrt{a})^2 = a$, and the distributive property.


Examples of Operations on Real Numbers

Example 1. Calculate $5\sqrt{2} + 3\sqrt{2} - \sqrt{2}$.

Answer:

These are terms involving the same irrational component, $\sqrt{2}$. We can treat the coefficients (5, 3, and -1) like coefficients in an algebraic expression and combine them.

$\quad 5\sqrt{2} + 3\sqrt{2} - 1\sqrt{2}$

Factor out the common irrational part $\sqrt{2}$:

$\quad = (5 + 3 - 1)\sqrt{2}$

Perform the arithmetic within the parentheses:

$\quad = 7\sqrt{2}$

The result is $\mathbf{7\sqrt{2}}$, which is an irrational number (a non-zero rational multiplied by an irrational).


Example 2. Calculate $(2 + \sqrt{3})(2 - \sqrt{3})$.

Answer:

This is a product of two binomials. We can use the distributive property (FOIL method) or recognize the pattern $(a+b)(a-b) = a^2 - b^2$. Here, $a=2$ and $b=\sqrt{3}$.

Using the difference of squares pattern:

$\quad (2 + \sqrt{3})(2 - \sqrt{3}) = (2)^2 - (\sqrt{3})^2$

Calculate the squares:

$\quad = 4 - 3$

Perform the subtraction:

$\quad = 1$

Using the distributive property:

$\quad (2 + \sqrt{3})(2 - \sqrt{3}) = 2(2) + 2(-\sqrt{3}) + \sqrt{3}(2) + \sqrt{3}(-\sqrt{3})$

$\quad = 4 - 2\sqrt{3} + 2\sqrt{3} - (\sqrt{3})^2$

$\quad = 4 + (-2\sqrt{3} + 2\sqrt{3}) - 3$

$\quad = 4 + 0 - 3$

$\quad = 1$

Both methods show that the result is $\mathbf{1}$, which is a rational number.


Example 3. Calculate $\sqrt{8} \times \sqrt{18}$.

Answer:

Use the property $\sqrt{a} \times \sqrt{b} = \sqrt{a \times b}$ for non-negative $a, b$.

$\quad \sqrt{8} \times \sqrt{18} = \sqrt{8 \times 18}$

Multiply the numbers under the radical:

$\quad = \sqrt{144}$

Calculate the square root of 144:

$\quad = 12$

The result is $\mathbf{12}$, which is a rational number. Note that both $\sqrt{8}$ and $\sqrt{18}$ are irrational numbers, but their product is rational.


Example 4. Calculate $\frac{10\sqrt{6}}{2\sqrt{2}}$.

Answer:

Separate the rational and irrational parts of the division:

$\quad \frac{10\sqrt{6}}{2\sqrt{2}} = \frac{10}{2} \times \frac{\sqrt{6}}{\sqrt{2}}$

Perform the rational division and use the property $\frac{\sqrt{a}}{\sqrt{b}} = \sqrt{\frac{a}{b}}$ for $a \ge 0, b > 0$ for the irrational part:

$\quad = 5 \times \sqrt{\frac{6}{2}}$

$\quad = 5 \times \sqrt{3}$

The result is $\mathbf{5\sqrt{3}}$, which is an irrational number.

Sometimes, you may need to rationalize the denominator in the quotient of irrational numbers if it contains a radical.


Rationalizing the Denominator

Rationalizing the denominator is the process of converting a fraction with an irrational number in the denominator into an equivalent fraction with a rational number in the denominator. This is often done to simplify expressions or to make calculations easier.

Example 5. Rationalize the denominator of $\frac{3}{\sqrt{5}}$.

Answer:

The denominator is $\sqrt{5}$. Multiply the numerator and denominator by $\sqrt{5}$.

$\quad \frac{3}{\sqrt{5}} = \frac{3}{\sqrt{5}} \times \frac{\sqrt{5}}{\sqrt{5}}$

Multiply numerators and denominators:

$\quad = \frac{3 \times \sqrt{5}}{\sqrt{5} \times \sqrt{5}} = \frac{3\sqrt{5}}{(\sqrt{5})^2} = \frac{3\sqrt{5}}{5}$

The denominator is now the rational number 5.


Example 6. Rationalize the denominator of $\frac{1}{2 + \sqrt{3}}$.

Answer:

The denominator is the binomial $2 + \sqrt{3}$. Its conjugate is $2 - \sqrt{3}$. Multiply the numerator and denominator by the conjugate.

$\quad \frac{1}{2 + \sqrt{3}} = \frac{1}{2 + \sqrt{3}} \times \frac{2 - \sqrt{3}}{2 - \sqrt{3}}$

Multiply the numerators and the denominators. The denominator is of the form $(a+b)(a-b) = a^2 - b^2$ with $a=2$ and $b=\sqrt{3}$.

$\quad = \frac{1 \times (2 - \sqrt{3})}{(2 + \sqrt{3})(2 - \sqrt{3})} = \frac{2 - \sqrt{3}}{(2)^2 - (\sqrt{3})^2}$

Calculate the squares and subtract in the denominator:

$\quad = \frac{2 - \sqrt{3}}{4 - 3} = \frac{2 - \sqrt{3}}{1}$

$\quad = 2 - \sqrt{3}$

The denominator is now the rational number 1.



Order of Operations (BODMAS/PEMDAS)

When a mathematical expression involves more than one arithmetic operation, the sequence in which these operations are performed is crucial for obtaining a unique and correct result. To standardize calculations, a fixed order of operations has been established and is universally followed. This order is commonly memorized using acronyms like BODMAS or PEMDAS.


The BODMAS Rule

In India and many other parts of the world, the acronym BODMAS is used to remember the standard order of operations. Each letter stands for a type of operation:

The sequence of performing operations is as follows:

  1. Evaluate any expressions contained within Brackets (Parentheses, Curly Braces $\{\}$, Square Brackets []). If there are brackets nested within other brackets, perform the operations in the innermost brackets first and work outwards.
  2. Evaluate all Orders, which include exponents (powers like $2^3$) and roots (like $\sqrt{9}$).
  3. Perform all Division and Multiplication operations. These two operations have the same level of priority. When both division and multiplication appear in an expression, perform them in the order they appear from left to right.
  4. Perform all Addition and Subtraction operations. These two operations also have the same level of priority. When both addition and subtraction appear in an expression, perform them in the order they appear from left to right.

It's important to remember that Division and Multiplication are on the same level (left to right) and Addition and Subtraction are on the same level (left to right).


The PEMDAS Rule

Another widely used acronym for the order of operations is PEMDAS, which stands for:

PEMDAS is effectively the same rule as BODMAS, just using slightly different terminology (Parentheses instead of Brackets, Exponents instead of Orders/Indices) and listing Multiplication before Division (M/D) and Addition before Subtraction (A/S). The priority levels and left-to-right evaluation for M/D and A/S remain the same. In the Indian context, BODMAS is generally the preferred acronym.


Examples Applying BODMAS

Example 1. Evaluate $10 + 2 \times (6 - 3)$.

Answer:

Apply the BODMAS rule step by step:

  1. B - Brackets: First, perform the operation inside the brackets: $(6 - 3) = 3$.
    The expression becomes: $10 + 2 \times 3$.
  2. O - Orders: There are no powers or roots in the expression.
  3. D/M - Division and Multiplication: Next, perform multiplication: $2 \times 3 = 6$.
    The expression becomes: $10 + 6$.
  4. A/S - Addition and Subtraction: Finally, perform addition: $10 + 6 = 16$.

The result is $\mathbf{16}$.


Example 2. Evaluate $25 \div 5 \times 2 + (3+1)^2 - 7$.

Answer:

Apply the BODMAS rule step by step:

  1. B - Brackets: First, perform the operation inside the brackets: $(3+1) = 4$.
    The expression becomes: $25 \div 5 \times 2 + 4^2 - 7$.
  2. O - Orders: Next, evaluate the power: $4^2 = 16$.
    The expression becomes: $25 \div 5 \times 2 + 16 - 7$.
  3. D/M - Division and Multiplication: These have equal priority, so work from left to right.
    First, Division: $25 \div 5 = 5$.
    The expression becomes: $5 \times 2 + 16 - 7$.
    Next, Multiplication: $5 \times 2 = 10$.
    The expression becomes: $10 + 16 - 7$.
  4. A/S - Addition and Subtraction: These have equal priority, so work from left to right.
    First, Addition: $10 + 16 = 26$.
    The expression becomes: $26 - 7$.
    Next, Subtraction: $26 - 7 = 19$.

The result is $\mathbf{19}$.

Note on Left-to-Right Rule for D/M and A/S:

  • In Step 3, if we had done Multiplication before Division (incorrectly applying strict order instead of left-to-right for equal priority), we might calculate $5 \times 2 = 10$ first, leading to $25 \div 10 + 16 - 7 = 2.5 + 16 - 7 = 18.5 - 7 = 11.5$, which is wrong. The left-to-right rule for equal priority operations is essential.
  • In Step 4, if we had done Subtraction before Addition, we might calculate $16 - 7 = 9$ first, leading to $10 + 9 = 19$. In this particular instance, it didn't change the final result, but relying on strict A before S order is incorrect. The left-to-right rule ensures the correct result in all cases (e.g., $10 - 5 + 3$ should be $(10-5)+3 = 5+3=8$, not $10-(5+3) = 10-8=2$).

Example 3. Evaluate $3 \times [2 + \{5 - (6 \div 2)\} + 4]$.

Answer:

Apply BODMAS, working from innermost brackets outwards:

  1. B - Innermost Brackets: Perform operation inside the innermost parentheses: $(6 \div 2) = 3$.
    The expression becomes: $3 \times [2 + \{5 - 3\} + 4]$.
  2. B - Next Level Brackets: Perform operation inside the curly braces: $\{5 - 3\} = 2$.
    The expression becomes: $3 \times [2 + 2 + 4]$.
  3. B - Outermost Brackets: Perform operations inside the square brackets: $[2 + 2 + 4] = 8$.
    The expression becomes: $3 \times 8$.
  4. O - Orders: None.
  5. D/M - Division/Multiplication: Perform multiplication: $3 \times 8 = 24$.
  6. A/S - Addition/Subtraction: None remaining.

The result is $\mathbf{24}$.

Consistently applying the order of operations (BODMAS/PEMDAS) is critical for accurately evaluating complex arithmetic expressions.



Simplification of Expressions involving various Number Types

Simplifying mathematical expressions that involve different types of numbers (such as integers, fractions, decimals, and irrational numbers like square roots) and multiple arithmetic operations requires a systematic approach. The key is to apply the rules for each specific operation correctly and strictly adhere to the established order of operations (BODMAS/PEMDAS).

While it's often helpful to convert all numbers within an expression to a single format (either fractions or decimals) before performing operations, sometimes the expression's structure or the nature of the numbers involved might make it simpler to work with mixed formats or keep irrational numbers in their symbolic form.


Steps for Simplifying Expressions

Here's a general approach to simplifying expressions with various number types:

  1. Understand the Expression: Identify all the numbers and the operations involved. Note the grouping symbols (brackets).
  2. Convert to a Common Format (Optional but Often Helpful): Decide whether to work with fractions, decimals, or a mix.
    • If the expression primarily contains fractions, converting decimals to fractions is usually a good idea.
    • If the expression primarily contains decimals or involves non-terminating repeating decimals where conversion to fraction is complex, working with decimals might be easier (you may need to round irrational numbers if an exact answer isn't possible).
    • Irrational numbers like $\sqrt{2}$ or $\pi$ can often be kept in their symbolic form until the final step, unless operations within brackets or orders require calculation involving their approximate values.
  3. Apply the Order of Operations (BODMAS/PEMDAS): Proceed through the operations in the specified order:
    • B - Brackets (Parentheses): Simplify expressions within all grouping symbols, starting from the innermost ones.
    • O - Orders (Exponents/Roots): Evaluate powers, roots, and other operations indicated by superscripts or radical signs.
    • D & M - Division and Multiplication: Perform all division and multiplication operations in the order they appear from left to right.
    • A & S - Addition and Subtraction: Perform all addition and subtraction operations in the order they appear from left to right.
  4. Perform Operations and Simplify: Execute the calculations according to the rules for the specific number types you are working with (fraction addition, decimal multiplication, integer subtraction, etc.). Simplify results at each stage where possible (e.g., reduce fractions to lowest terms).

Examples of Simplification

Example 1. Simplify $2\frac{1}{2} + \frac{3}{4} \times (\frac{5}{6} - \frac{1}{3})$.

Answer:

This expression involves a mixed number and fractions. Let's convert the mixed number to an improper fraction to work entirely with fractions: $2\frac{1}{2} = \frac{(2 \times 2) + 1}{2} = \frac{5}{2}$.

The expression becomes: $\frac{5}{2} + \frac{3}{4} \times (\frac{5}{6} - \frac{1}{3})$.

Now, apply BODMAS:

  1. B - Brackets: First, evaluate the expression inside the parentheses: $(\frac{5}{6} - \frac{1}{3})$. Find a common denominator for 6 and 3. LCM$(6, 3) = 6$. Convert $\frac{1}{3}$ to sixths: $\frac{1 \times 2}{3 \times 2} = \frac{2}{6}$.
    Subtract: $\frac{5}{6} - \frac{2}{6} = \frac{5-2}{6} = \frac{3}{6}$.
    Simplify the result inside the brackets: $\frac{3}{6} = \frac{1}{2}$.
    The expression becomes: $\frac{5}{2} + \frac{3}{4} \times \frac{1}{2}$.
  2. O - Orders: There are no powers or roots.
  3. D/M - Division and Multiplication: Next, perform the multiplication: $\frac{3}{4} \times \frac{1}{2}$. Multiply the numerators and the denominators.
    $\frac{3}{4} \times \frac{1}{2} = \frac{3 \times 1}{4 \times 2} = \frac{3}{8}$.
    The expression becomes: $\frac{5}{2} + \frac{3}{8}$.
  4. A/S - Addition and Subtraction: Finally, perform the addition: $\frac{5}{2} + \frac{3}{8}$. Find a common denominator for 2 and 8. LCM$(2, 8) = 8$. Convert $\frac{5}{2}$ to eighths: $\frac{5 \times 4}{2 \times 4} = \frac{20}{8}$.
    Add: $\frac{20}{8} + \frac{3}{8} = \frac{20+3}{8} = \frac{23}{8}$.

The simplified fraction is $\mathbf{\frac{23}{8}}$. This can also be written as a mixed number $2\frac{7}{8}$.


Example 2. Simplify $15 \div 0.5 + (2.4 \times 3) - \sqrt{16}$.

Answer:

This expression involves an integer, decimals, multiplication, division, addition, subtraction, and a square root. Let's evaluate the root and work with decimals where convenient.

The expression is $15 \div 0.5 + (2.4 \times 3) - \sqrt{16}$.

Apply BODMAS:

  1. B - Brackets: Evaluate the expression inside the parentheses: $(2.4 \times 3)$. Multiply as if they were whole numbers: $24 \times 3 = 72$. Count decimal places: 2.4 has 1, 3 has 0. Total 1. Place decimal in 72 to get 1 decimal place: 7.2.
    So, $(2.4 \times 3) = 7.2$.
    The expression becomes: $15 \div 0.5 + 7.2 - \sqrt{16}$.
  2. O - Orders: Evaluate the square root: $\sqrt{16} = 4$.
    The expression becomes: $15 \div 0.5 + 7.2 - 4$.
  3. D/M - Division and Multiplication: Perform the division $15 \div 0.5$. Convert the divisor to a whole number by multiplying by 10: $0.5 \times 10 = 5$. Multiply the dividend by 10: $15 \times 10 = 150$. Now divide $150 \div 5 = 30$.
    The expression becomes: $30 + 7.2 - 4$.
  4. A/S - Addition and Subtraction: Perform addition and subtraction from left to right.
    First, Addition: $30 + 7.2 = 37.2$.
    The expression becomes: $37.2 - 4$.
    Next, Subtraction: $37.2 - 4 = 33.2$.

The simplified value is $\mathbf{33.2}$.

Alternative Approach (using fractions):

Convert decimals and root to fractions:

$0.5 = \frac{5}{10} = \frac{1}{2}$. $2.4 = \frac{24}{10} = \frac{12}{5}$. $\sqrt{16} = 4 = \frac{4}{1}$.

The expression is $15 \div \frac{1}{2} + (\frac{12}{5} \times \frac{3}{1}) - 4$.

Apply BODMAS:

  1. B - Brackets: $(\frac{12}{5} \times \frac{3}{1}) = \frac{12 \times 3}{5 \times 1} = \frac{36}{5}$.
    Expression: $15 \div \frac{1}{2} + \frac{36}{5} - 4$.
  2. O - Orders: None.
  3. D/M - Division: $15 \div \frac{1}{2} = \frac{15}{1} \times \frac{2}{1} = \frac{30}{1} = 30$.
    Expression: $30 + \frac{36}{5} - 4$.
  4. A/S - Addition and Subtraction: Convert 30 and 4 to fractions with denominator 5: $30 = \frac{150}{5}$, $4 = \frac{20}{5}$.
    Expression: $\frac{150}{5} + \frac{36}{5} - \frac{20}{5}$.
    Combine numerators: $\frac{150 + 36 - 20}{5} = \frac{186 - 20}{5} = \frac{166}{5}$.

The simplified fraction is $\frac{166}{5}$. Convert to decimal: $166 \div 5 = 33.2$. Both methods yield the same result.

Practicing with expressions involving different number types and operations is crucial for building fluency and accuracy in numerical applications.