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Least common multiple review

Review least common multiples (LCM) and try some practice problems.

What is LCM?

LCM stands for least common multiple. The least common multiple of two numbers is the smallest number that is a multiple of both of them.

Finding least common multiple

One way to find the LCM of two (or more!) numbers is to list the multiples of each number until we find the smallest multiple they have in common.
Want to learn more about least common multiples? Check out this video.

Example 1: LCM of 8 and 10

Multiples of 8: 8,16,24,32,40,48,56,64,72,80
Multiples of 10: 10,20,30,40,50,60,70,80,90,100
40 and 80 are common multiples of 8 and 10. Which of these is the least?
40 is the smallest multiple that 8 and 10 have in common.

Example 2: LCM of 3,4, and 6

Multiples of 3: 3,6,9,12,15,18,21,24
Multiples of 4: 4,8,12,16,20,24,28
Multiples of 6: 6,12,18,24,30,36
12 is the smallest multiple that 3,4, and 6 have in common.


Problem 1
What is the least common multiple of 3 and 9?
Another way to say this is:
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi

Want to try more problems like this? Check out this exercise.

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