7 , 21 , 63

The LCM is the smallest positive number that all of the numbers divide into evenly.

1. List the prime factors of each number.

2. Multiply each factor the greatest number of times it occurs in either number.

Since 7 has no factors besides 1 and 7.

7 is a prime number

21 has factors of 3 and 7.

3⋅7

63 has factors of 3 and 21.

3⋅21

21 has factors of 3 and 7.

3⋅3⋅7

3⋅3⋅7

Multiply 3 by 3.

9⋅7

Multiply 9 by 7.

63

63

Find the LCM 7 , 21 , 63