## 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**

1x 12 = 12

2x 6 = 12

3x 4 = 12

4x 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**

1x 20 = 20

2x 10 = 20

3isn’t a factor, so we move on to 4.

4x 5 = 20

5x 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.