5/27/22, 3:27 AM Least Common Multiple
Addition and Subtraction:
Least Common Multiple
When we learned adding and subtracting fractions, we learned that the number on the bottom,
the denominator, has to be the same. In order to get a common denominator, we first need to
find the Least Common Multiple (LCM). The LCM of 2 numbers is the smallest number that both
numbers divide evenly. The video below will explain 2 methods of finding LCMs:
0::44 1x
Video Source (08:44 mins) | Transcript
The 2 ways to find the LCM:
1. Skip Counting
List the multiples of each of the numbers given and find the smallest number in both lists.
2. Prime Factorization
Find all the prime factors of each number given.
Create a new number that contains all the prime factors of each number. Remember to
include multiples If there are multiples of the same factor in either prime factorization.
Example: 9 = 3 × 3 and 15 = 3 × 5, since 9 has two 3s and 15 has only one 3 in its
factorization, the combined list will need two 3’s. The LCM of 9 and 15 is 3 × 3 × 5 = 45
Additional Resources
Khan Academy: Least Common Multiple (04:15 mins, Transcript)
Khan Academy: Least Common Multiple with Repeating Factors (02:34 mins, Transcript)
https://content.byui.edu/file/b8b83119-9acc-4a7b-bc84-efacf9043998/1/Math-1-8-1.html 1/2
Addition and Subtraction:
Least Common Multiple
When we learned adding and subtracting fractions, we learned that the number on the bottom,
the denominator, has to be the same. In order to get a common denominator, we first need to
find the Least Common Multiple (LCM). The LCM of 2 numbers is the smallest number that both
numbers divide evenly. The video below will explain 2 methods of finding LCMs:
0::44 1x
Video Source (08:44 mins) | Transcript
The 2 ways to find the LCM:
1. Skip Counting
List the multiples of each of the numbers given and find the smallest number in both lists.
2. Prime Factorization
Find all the prime factors of each number given.
Create a new number that contains all the prime factors of each number. Remember to
include multiples If there are multiples of the same factor in either prime factorization.
Example: 9 = 3 × 3 and 15 = 3 × 5, since 9 has two 3s and 15 has only one 3 in its
factorization, the combined list will need two 3’s. The LCM of 9 and 15 is 3 × 3 × 5 = 45
Additional Resources
Khan Academy: Least Common Multiple (04:15 mins, Transcript)
Khan Academy: Least Common Multiple with Repeating Factors (02:34 mins, Transcript)
https://content.byui.edu/file/b8b83119-9acc-4a7b-bc84-efacf9043998/1/Math-1-8-1.html 1/2
