New News Maths #7

Highest Common Factor

Highest Common Factor (HCF) = the biggest factor a set of numbers have in common

Example: Find the HCF of ‘28’ & ‘20’ (list out the factors of both numbers)

‘20’ ‘28’

1 1

2 2

4 4

5 7

10 14

20 28

The HCF of ‘28’ & ‘20’ is ‘4’

Example: Find the HCF of ‘12’ & ‘18’ (Using the prime factors)

Of 12: 2 * 2 * 3

Of 18: 2 * 3 * 3

Select the prime factors that occur in both lists.

2*3=6 (‘6’ is the HCF of ‘12’ & ‘18’)