HCF - Highest Common Factor, the largest whole number that each number can be divided by

LCM - Lowest Common Multiple, the smallest number that both numbers evenly divide into e.g. 6 and 8 LCM = 24

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HCF Method:

E.g. 72 and 90

The biggest number that both 

72 = 2x2x2x3x3

90 = 2x3x3x5

HCF = 2x3x3 = 18

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LCM Method:

E.g. 72 and 90

Find the prime factors, but only use the number with the most appearances of each factor

So 90 = 3x3x2x5 and 72 = 3x3x2x2x2 LCM = 2^3 x 3^2 x 5 = 360 

This only uses the 3's from 90, the 2's from 72 and the 5 from 72.

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