Solution: The LCM of 28 and 90 is 1260
Methods
How to find the LCM of 28 and 90 using Prime Factorization
One way to find the LCM of 28 and 90 is to start by comparing the prime factorization of each number. To find the prime factorization, you can follow the instructions for each number here:
What are the Factors of 28?
What are the Factors of 90?
Here is the prime factorization of 28:
2
2
×
7
1
2^2 × 7^1
2 2 × 7 1
And this is the prime factorization of 90:
2
1
×
3
2
×
5
1
2^1 × 3^2 × 5^1
2 1 × 3 2 × 5 1
When you compare the prime factorization of these two numbers, you want to look for the highest power that each prime factor is raised to. In this case, there are these prime factors to consider: 2, 7, 3, 5
2
2
×
3
2
×
5
1
×
7
1
=
1260
2^2 × 3^2 × 5^1 × 7^1 = 1260
2 2 × 3 2 × 5 1 × 7 1 = 1260
Through this we see that the LCM of 28 and 90 is 1260.
How to Find the LCM of 28 and 90 by Listing Common Multiples
The first step to this method of finding the Least Common Multiple of 28 and 90 is to begin to list a few multiples for each number. If you need a refresher on how to find the multiples of these numbers, you can see the walkthroughs in the links below for each number.
Let’s take a look at the multiples for each of these numbers, 28 and 90:
What are the Multiples of 28?
What are the Multiples of 90?
Let’s take a look at the first 10 multiples for each of these numbers, 28 and 90:
First 10 Multiples of 28: 28, 56, 84, 112, 140, 168, 196, 224, 252, 280
First 10 Multiples of 90: 90, 180, 270, 360, 450, 540, 630, 720, 810, 900
You can continue to list out the multiples of these numbers as long as needed to find a match. Once you do find a match, or several matches, the smallest of these matches would be the Least Common Multiple. For instance, the first matching multiple(s) of 28 and 90 are 1260, 2520, 3780. Because 1260 is the smallest, it is the least common multiple.
The LCM of 28 and 90 is 1260.
Find the LCM of Other Number Pairs
Want more practice? Try some of these other LCM problems:
What is the LCM of 83 and 19?
What is the LCM of 32 and 114?
What is the LCM of 136 and 94?
What is the LCM of 82 and 13?
What is the LCM of 150 and 93?