1. Factors

• What is the factors?

What does the symbol “÷” and “ = ” mean?

12÷3 = 418÷9 = 2

15÷4 = 3R3

Review

The symbol “ ” is “ division”The symbol “ = ” is “ division”

Therefore

12÷3 = 4We can read that “ twelve divide

three equals four

• 18÷9 = 2• We can read that “ eight divide nine

equals two

• What about?

15÷4 = ?

12÷3 = 4

If 12 can be divided by 3, so 3 is a factor of 12

18÷9 = 2

If 18 can be divided by 9, so 9 is a factor of 18

15÷4 = 3.75

If 15 cannot be divided by 4, so 4 is not a factor of 15

(A) Determine whether the given number is a factor of the number in brackets.

• (a). 2 (14)• (b). 5 (120)• (c). 8 (124)• (d). 12 (106)• (e). 15 (145)• (f). 21 (105)

(B) List the factors of a whole number

24

2 12

2 6

2 3

List down all the factors of 24

1

24 can be divided by 2, 3, 6, 12 and 24.So, the factors of 24 are 2, 3, 6, 12 and 24.

2. Prime factors• (A) Prime numbers

A prime number is a whole number that

has only two factors, that is 1 and itself.

Example

•Determine whether the following are prime numbers: 4, 6, 7, 9, and 13

• 4 has three factors: 1, 2,and 4

4 prime number.

• 7 has two factors: 1 and 7

7 is a prime number

• 9 has three factors: 1, 3 and 9

9 is not a prime number

• 13 has two factors: 1 and 13

13 is a prime number

• prime numbers from 1-100have 25 numbers:

          2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97

Greatest Common Divisor (GCD)

Example Find the common divisor and the greatest common factor (GCD) of 8 and 20 factor of 8 = 1, 2, 4 and 8. factor of 20 are 1, 2, 4, 5, 10 and 20 1, 2, 4 are the common divisors of 8 and 20 4 is the greatest common divisor of 8 and 20

Exercise 1

• Find the GCD of following pairs of number.• 1) 2, 15……………..• 2) 5, 10……………..• 3) 12, 2……………..• 4) 8, 40……………..• 5) 6, 8………………..

Least common multiple(LCM)

• 1.) 4 and 8 LCM=• 2.) 12 and 18 LCM=