# What is the GCF of 9 and 21?

GCF (Greatest Common Factor) of two numbers is the largest number that divides the two numbers exactly leaving the remainder 0

## Answer: GCF of 9 and 21 is 3

Lets see how to find the GCF of 9 and 21

## Explanation:

We can find the GCF by any of the following two methods.

- Listing the common factors method
- Prime factorization Method

### Find GCF of 9 and 21 by Listing the Common Factors

The factors of 9 and 21 are shown below.

Factors of 9: 1, 3, 9

Factors of 21: 1, 3, 7, 21

The common factors of 9 and 21 are 1 and 3

Clearly, the greatest common factor of 9 and 21 is 3

So, GCF of 9 and 21 is 3

### GCF of 9 and 21 by Prime Factorization

We will represent 9 and 21 as a product of their prime factors.

Look at the prime factorization of 9 and 21

Prime factorization of 9 is 3 × 3

Prime factorization of 21 is 3 × 7

Common prime factor = 3

GCF is the product of the factors that are common to each of the given numbers.

GCF of 9 and 21 is 3

Irrespective of the method, the solution to our question GCF of 9 and 21 is the same.