# What is the LCM of 21 and 15?

To find the LCM of 21 and 15, we need the least number which is exactly divisible by both 15 and 21.

## Answer: LCM of 21 and 15 is 105

The Least Common Multiple of two numbers a and b is the smallest number that divides a and b exactly.

## Explanation:

We can find the LCM of the numbers in many ways.

### LCM of 21 and 15 by Listing Method

We will list the first few multiples of 21 and 15 and determine the common multiples.

The least among the common multiples is the LCM of 21 and 15

105 is the least common multiple of 21 and 15

### LCM of 21 and 15 by Formula

The formula of LCM is

LCM (a,b) = (a × b) / GCF (a,b)

The Greatest Common Factor of (21,15) is 3. So, GCF (21,15) = 3

So, the LCM of 21 and 15 by using the formula,

LCM (21,15) = (21 × 15) / 3

= 315 / 3

= 105

LCM of 21 and 15 = 105

Observe that the solution to our question LCM of 21 and 15 is the same in both methods.