Q:

What is the LCM of 21 and 120?

Accepted Solution

A:
Solution: The LCM of 21 and 120 is 840 Methods How to find the LCM of 21 and 120 using Prime Factorization One way to find the LCM of 21 and 120 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 21? What are the Factors of 120? Here is the prime factorization of 21: 3 1 × 7 1 3^1 × 7^1 3 1 × 7 1 And this is the prime factorization of 120: 2 3 × 3 1 × 5 1 2^3 × 3^1 × 5^1 2 3 × 3 1 × 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: 3, 7, 2, 5 2 3 × 3 1 × 5 1 × 7 1 = 840 2^3 × 3^1 × 5^1 × 7^1 = 840 2 3 × 3 1 × 5 1 × 7 1 = 840 Through this we see that the LCM of 21 and 120 is 840. How to Find the LCM of 21 and 120 by Listing Common Multiples The first step to this method of finding the Least Common Multiple of 21 and 120 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, 21 and 120: What are the Multiples of 21? What are the Multiples of 120? Let’s take a look at the first 10 multiples for each of these numbers, 21 and 120: First 10 Multiples of 21: 21, 42, 63, 84, 105, 126, 147, 168, 189, 210 First 10 Multiples of 120: 120, 240, 360, 480, 600, 720, 840, 960, 1080, 1200 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 21 and 120 are 840, 1680, 2520. Because 840 is the smallest, it is the least common multiple. The LCM of 21 and 120 is 840. Find the LCM of Other Number Pairs Want more practice? Try some of these other LCM problems: What is the LCM of 94 and 11? What is the LCM of 40 and 117? What is the LCM of 128 and 111? What is the LCM of 97 and 63? What is the LCM of 60 and 5?