HCF & LCM - 1st Sep 2008

We looked at how to find the Highest Common Factor (HCF) and Lowest Common Multiple (LCM) of two numbers by finding the prime factors of both numbers and using a Venn diagram.

For example to find the HCF and LCM of 84 and 140:

1. Use factor trees to find the prime factors of both numbers

2. Put the prime factors of both numbers in a Venn diagram. Any prime factors in common go in the centre and others go to the sides.

3. To work out the Highest Common Factor, multiple the numbers in the overlapping area together

HCF = 2 x 2 x 7 = 28

4. To work out the Lowest Common Multiple, Multiple all the numbers in the Venn diagram together.

LCM = 3 x 2 x 2 x 7 x 5 = 420

You can find more details and other examples on the Mymaths.co.uk lessons for HCF and LCM.

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