Home / United States / Math Classes / 6th Grade Math / Least Common Multiple

Two numbers may have several common multiples. The least common multiple, or the LCM, has some special significance as we use it quite often for simplification of equations. Learn how to find the LCM of two numbers with the help of some solved examples. ...Read MoreRead Less

We can find multiples of a number when we multiply a given number with an integer.

For example:

This implies that two or more numbers can have the same multiples. They are referred to as common multiples.

For example: 3 and 4 have the following common multiples as shown in the figure below:

The least among all common multiples of two or more numbers is referred to as the Least Common Multiple or LCM. LCM of two or more numbers can be evaluated through the following ways:

1. Listing of multiples

2. Prime Factorization

Let us consider some examples to have a better understanding of these concepts:

**An example using the listing of multiples :**

Find the LCM of 3 and 4.

**Solution:**

List all the multiples of 3 and 4 and select the least among them.

Multiples of 3 are: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30

Multiples of 4 are: 4, 8, 12, 16, 20, 24, 28, 32, 36, 40

The figure above denotes the three common multiples at the intersection of the two circles. Clearly, the least among them is 12. Hence, the LCM of 3 and 4 is 12.

**An example using Prime Factorization:**

Find the LCM of 12 and 14

**Solution:**

Let’s find the prime factors of 12 and 14 respectively, using the factor tree.

So, 12 = 2 \( \times \) 2 \( \times \) 3

And, 14 = 2 \( \times \) 7

Now, select each factor where it appears the greater number of times, so select 2, 2 and 3 from the factors of 12, and select 7 from the factors of 14. Do not Select 2 again from the factors of 14, as we have selected it from factors of 12.

Now,

LCM of 12 and 14 is the product of the selected factors

LCM of 12 and 14 = 2 \( \times \) 2 \( \times \) 3 \( \times \) 7

= 84

**An examples of finding the LCM of more than two numbers:**

Find the LCM of 15, 25 and 50:

**Solution:**

Prime Factors of 15, 25 and 50 are:

15 = 3 \( \times \) 5

3 appears only once here, so highlight it,

25 = 5 \( \times \) 5

5 appears most often here,

50 = 2 \( \times \) 5 \( \times \) 5

2 appears only once here, so highlight it,

LCM = 2 \( \times \) 3 \( \times \) 5 \( \times \) 5

So the LCM of 15, 25 and 50 is 150.

Ryan and Lisa are on a running track. Ryan completes one lap in 4 minutes and Lisa completes it in 6 minutes. If they start together, after how many minutes will they meet again at the starting point?

**Solution :**

You are given the number of minutes Ryan and Lisa take to complete a round. The LCM of the number of minutes will give us the time when they will meet again at the starting point. So, let’s find the LCM of 4 and 6.

Multiples of 4: 4, 8, 12, 16, 20, 24, 28, 32, 36, 40

Multiples of 6: 6, 12, 18, 24, 30, 36, 42, 48, 54, 60

Clearly the LCM of 4 and 6 is 24.

Hence, Ryan and Lisa will meet again at the starting point after 24 minutes.

Frequently Asked Questions

The multiples of a number are infinite, so we cannot find the greatest common multiple of two or more numbers.

For any two numbers, the product of the GCF (Greatest common factor) and the LCM is equal to the product of the two numbers.