Highest Common Factor (HCF)

Remember:
Factors divide EXACTLY into another number – so no fractions!

Be systematic and pair up your factors – start with 1 (as shown below in bold) and then go up until you find you repeating yourself. e.g. factors of 12 and 20.

Factors of 12

1 x 12 = 12
2 x 6 = 12
3 x 4 = 12
4 x 3 = 12… (this is a repeat of the previous line, so we can stop finding any more factors.)

So, the factors of 12 are: 1, 2, 3, 4, 6 and 12.

To find the factors of 20, repeat the process:

Factors of 20

1 x 20 = 20
2 x 10 = 20
3 isn’t a factor, so we move on to 4.
4 x 5 = 20
5 x 4 = 20… again, this is a repeat of the previous line, so we can stop.

The factors of 20 are: 1, 2, 4, 5, 10, and 20.

 

 

The common factors are the numbers in both lists – i.e. 1, 2, and 4.

The Highest Common Factor will be the highest of these numbers, in this case 4.