Find Factors and Highest Common Factors

In this activity, we'll be getting to grips with finding the highest common factor. 

But first, let's have a look at what we mean by the word factor.

A number that divides exactly into another number with no remainders is called a factor of that number. 

For example, to make 15 we can do 1 x 15  or  3 x 5  so the list of factors are 1, 3, 5 and 15. 

Here's a factor bug showing us the different factors.

To find the factors of 12 we can do the same thing again.  We should think about the numbers which when multiplied together make 12. 

1 x 12    2 x 6     3 x 4    so the list of numbers are 1, 2, 3, 4, 6 and 12. 

The highest common factor for a set of numbers is found by identifying the factor they have in common with the highest value.

For example, the highest common factor for 15 and 12 would be 3.

Here's another example to look at.  Let's find the highest common factor for 15 and 20.   

The factors for 15 are 1, 3, 5 and 15  and the factors for 20 are 1, 2, 4, 5, 10 and 20 

The highest common factor of 15 and 20 is 5. 

Are you ready to try some questions now?