# Math help from the Learning Centre

This guide provides useful resources for a wide variety of math topics. It is targeted at students enrolled in a math course or any other Centennial course that requires math knowledge and skills.

## Commutative Law

The Commutative Law states that even if we switch the order of the numbers, the resulting answer is the same. The commutative law holds for addition and multiplication.

The Commutative Law of Addition: a + b = b + a

Example The Commutative Law of Multiplication: a × b = b × a

Example The commutative law does not hold for subtraction or division.

For instance:

• 3 - 2 ≠ 2 - 3
• 2 ÷ 3 ≠ 3 ÷ 2

Uses of Commutative Law

It is sometimes easier to compute the answer to a multiplication or addition question by switching the order of numbers.

Example

For addition question: In the question 3 + 44 + 17, it is easier if we add 17 and 3 first, so 3 + 44 + 17 = 44 + 3 + 17 = 44+20 = 64

Example

For multiplication question: In the question, 5 × 10 × 6, it is easier if we multiply 6 and 5 first, so 5 × 10 × 6 = 10 × 5 × 6 = 10 × 30 = 300

## Associative Law

The Associative Law states that even if we group numbers differently, the answer is still the same. The associative law holds for addition and multiplication.

The Associative Law of Addition: (a + b) + c = a + (b + c)

Example The Associative Law of Multiplication: (a × b) × c = a × (b × c)

Example The associative law does not hold for subtraction or division.

For instance,

• (5 - 10) - 4 = -5 - 4 = -9 but 5 - (10 - 4) = 5 - 6 = -1
• (8 ÷ 4) ÷ 2 = 2 ÷ 2 = 1 but 8 ÷ (4 ÷ 2) = 8 ÷ 2 = 4

Uses of Associative Law

It is sometimes easier to add or multiply if we group numbers differently.

Example

For addition: In the question, 23 + 45 + 5, it is easier to add 45 and 5 first, rather than adding 23 and 45 first. So, 23 + 45 + 5 = 23 + (45 + 5) = 23 + 50 = 73

Example

For multiplication: In the question, 15 × 5 × 2, it is easier to first multiply 5 and 2 rather than 15 and 5. So, 15 × 5 × 2 = 15 × (5 × 2) = 15 × 10 = 150

## Distributive Law

The Distributive Law: a × (b + c) = a × b + a × c and a × (b - c) = a × b - a × c.

Example The distributive law does not hold for division.

For instance, 16 ÷ (8 + 2) = 16 ÷ 10 = 1.6 but 16 ÷ 8 + 16 ÷ 2 = 2 + 8 = 10.

The correct way is 16 ÷ (8 + 2) = 16 ÷ 10 = 1.6.

Uses of Distributive Law

A difficult multiplication question’s numbers can be broken up or combined, resulting in an easier multiplication question using the distributive law.

Example where we break up a number: In the question, 3 × 502, 502 can be broken up into (500 + 2) and so the question becomes, 3 × (500 + 2) and using the distributive law, this is equal to 3 × 500 + 3 × 2 = 1500 + 6 = 1506

Example where we combine numbers: In the question, 15 × 3 + 15 × 7, we can combine 3 and 7, so 15 × 3 + 15 × 7 = 15 × (3 + 7) = 15 × 10 = 150