How do you find the LCM and HCF of a set of numbers?

Answer 1

A Factor Is A Number That Divides Into Another Number Exactly. E.g. The Factors Of 12 Are 1, 2, 3, 4, 6 And 12.

If You Were Trying To Find The Highest Common Factor You Write Out The Factors Of All Numbers. E.g. 20 And 30.

Factors Of 20: 1, 2, 4, 5, 10 And 20.

Factors Of 30: 1, 2, 3, 5, 6, 10, 15 And 30.

So The Highest Common Factor Of 20 And 30 Is 10 Because It Is The Highest Factor That Appears In Both Factor Lists.

It Is The Same For The LCM Except You Write Out The Multiples Of The numbers Instead. E.g. 5 And 6.

Multiples Of 5: 5, 10, 15, 20, 25, 30, 35, 40, 45, And 50.

Multiples Of 6: 6, 12, 18, 24, 30, 36, 42, 48, 54 And 60.

So The Lowest Common Multiple Is 30. It Appears In Both Lists And Is The Lowest.

An easy way to find the HCF of a pair of numbers is listing out the prime factors. A way to do that is to use a factor tree. Find the common prime factors and multiply them together. e.g. if the prime factors were (2,2,3,3,3,5) and (2,3,3,5,5,7) then you would multiply 2,3,3 and 5.