In this activity, we will learn how to list some common multiples of two numbers.

 

Example

Write down the first four numbers that are multiples of both 6 and 8.

 

Answer

If we start by listing the multiples of 6 and 8, we can see if there are any common multiples.

Multiples of 6: 6, 12, 18, 24, 30, 36, 42, 48 etc

Multiples of 8: 8, 16, 24, 32, 40, 48 etc.

We can see that we have two common multiples already: 24 and 48.

 

We don't have to continue listing them all unless we want to because we can use the two that we have found to work out the next ones!

If we find multiples of 24, we know that they will also be common multiples of both 6 and 8!

24 x 2 = 48 which we already know is a common multiple of 6 and 8!

24 x 3 = 72

24 x 4 = 96 etc.

 

So, the first four common multiples of 6 and 8 are 24, 48, 72 and 96.

 

 

Example 2

Write down the first four numbers that are multiples of both 9 and 7.

 

Answer

If they have no common factor, as in this case, just multiply the two numbers together to get the first common multiple.  

9 x 7 = 63

Then write down multiples of this number.

63 x 2 = 126

63 x 3 = 189

63 x 4 = 252

The first four common multiples of 9 and 7 are: 63, 126, 189, 252

 

Let's have a go at some questions now.