MultiplesIf a number divides exactly into another number, the second is a multiple of the first.

Example3, 6, 9, 12, 15, 18

Example10, 12, 14, 16, 18, 20

are the first six multiples of 3

are the set of multiples of 2 between 10 and 20 inclusive

Example

From the set {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}

Write down the multiples of

(i) 2

(ii) 4

(iii) 6

Lowest Common Multiple (LCM)

Example

Find the lowest common multiple of 12 and 15.

That is the smallest common multiple of the two numbers

Example

Find the lowest common multiple of 9 and 12.

FactorsA factor is a number that will divide exactly into a given number

Example

List all the factors of

(i) 6

(ii) 12

(iii) 30

(iv) 19

Prime numbers

A prime number is a number that can be divided exactly by itself and

one only.

In other words it has only two factors

Example

List the first 8 prime numbers.

Prime Factors

When we want to express a number as a product of its prime factors

we express the number as a multiplication of prime numbers

Example

Express 48 in terms of its prime factors

Example

Express each of the following as products of prime numbers

a) 100

b) 42

c) 72

d) 84

e) 144

Highest common factor (HCF)

The highest common factor of two or more numbers is the greatest

number which will divide exactly into each of them.

Example

Find the HCF of 4, 6 and 8

Example

Find the HCF of

a) 6, 9 and 12

b) 12 and 18