Arithmetic Grade Four

Lesson Eighty: Least Common Multiples

In the next unit we will need to be able to find the least common multiple (LCM) of two numbers in order to solve certain problems involving fractions. Here's the basic information on LCMs.

Least Common Multiples
Finding the Least Common Multiple (LCM) of two numbers is quite similar to finding the GCF. Here are the steps for finding the LCM of 8 and 10.

Step One: List a few multiples of each number:

8: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88...
10: 10, 20, 30, 40, 50, 60, 70, 80, 90...

Step Two: Find the first match. In the case of 8 and 10, the first match is 40. So, that's your answer.

Here's another example 


  FIND THE LCM OF 3 and 9:

  STEP ONE: List some multiples of each number.

    3: 3, 6, 9, 12, 15, 18, 21, 24
    9: 9, 18, 27, 36, 45, 54, 63

  STEP TWO: Find the first match.

       9 (the number nine appears in both lists of multiples)
Now you get to try a few

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