What’s in common?
What is the lowest common multiple?
The lowest common multiple (LCM) of two numbers is the smallest whole number which is a multiple of both. A quick reminder, a multiple is a number that can be divided by another number a certain number of times without a remainder.
One of the basic rules to finding the LCM is to list the multiples of the larger number and stop when you get to a multiple of the smaller number. For example:
What is the LCM of 3 and 8?
Multiples of 3 are 3, 6, 9, 12, 15, 18, 21, 24 and so on.
Multiples of 8 are 8, 16, 24, 32, 40 and so on.
So the LCM of 3 and 8 is 24.
But what if you have a group of three or more numbers? For example:
What is the LCM of 6, 15 and 20?
Start writing out the multiples like this:
– Multiples of 6 are 6, 12, 18, 24, 30, 36
– Multiples of 15 are 15, 30, 45, 60
– Multiples of 20 are 20, 40, 60, 80
• Both 6 and 15 have multiples of 30, however 20 cannot have a multiple of 30. Both 15 and 20 have a multiple of 60. We know that 6 also has a multiple of 60, because 6 x 10 = 60.
• Because 60 is the only multiple all three numbers have in common, 60 is the lowest common multiple of the three numbers.
Here’s a few for you to try to get the hang of finding the LCM of two or more numbers: