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Factors and multiples

Highest common factor (HCF)

We have already seen that the factors of 24 are

1, 2, 3, 4, 6, 8, 12 and 24

and that the factors of 40 are

1, 2, 4, 5, 8, 10, 20 and 40.

The numbers 1, 2, 4 and 8 appear in both lists, so they are known as the common factors of 24 and 40.

The number 8 is the highest of them, and it is called the highest common factor (HCF).


What is the HCF of 12 and 20?

toggle answer


The factors of 12 are 1, 2, 3, 4, 6 and 12

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

The HCF of 12 and 20 is 4.

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