Lesson 3: Least Common Multiple6.NOS.4

I can…

I can find the least common multiple (LCM) of two numbers by listing or comparing their multiples.

Key words

• Multiple — What you get when you multiply a number by 1, 2, 3, and so on.
• Least common multiple — The smallest number that two or more numbers both go into.
• Common multiple — A number that two or more numbers both go into.
• Skip counting — Counting by a number, like 2, 4, 6, to list its multiples.
• Prime factorization — Writing a number as prime numbers multiplied together. It helps you find the LCM.

Steps

1. I want the LCM of 4 and 6. I skip count the multiples of 4: 4, 8, 12, 16, 20, 24.
2. Then I skip count the multiples of 6: 6, 12, 18, 24.
3. I look for the first number in BOTH lists. 12 is in both lists, and it comes before 24.
4. So the LCM of 4 and 6 is 12. I check: 12 ÷ 4 = 3 and 12 ÷ 6 = 2, so both go into 12 evenly.

Try it

What is the LCM of 9 and 12?

Check your answer

36

Multiples of 9: 9, 18, 27, 36, ... Multiples of 12: 12, 24, 36, ... The smallest common multiple is 36.

Sentence starter

I know ___ because ___.

Goal: I can explain how I found the LCM using the words multiple, common multiple, skip counting, and least common multiple.