Lesson 12: 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

• Least Common Multiple — The least positive number that is a multiple of two or more numbers.
• Multiple — What you get when you multiply a number by 1, 2, 3, and so on.
• 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

For a family party, paper plates come in packs of 8 and cups come in packs of 12. What is the least number of plates and cups you can buy so you have the same number of each?

Check your answer

24

Multiples of 8: 8, 16, 24, ... Multiples of 12: 12, 24, ... The smallest common multiple is 24, so buy 24 plates and 24 cups.

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.