# What is the GCF of 18 and 21?

The largest possible number which divides the given numbers exactly without any remainder is called the greatest common factor or the highest common factor of the given numbers.

## Answer: The GCF or HCF of 18 and 21 is 3

## Explanation:

The common methods of finding the GCF are prime factorization, listing the common factors. Let us see the methods in detail.

## Methods to find GCF of 18 and 21

We can calculate the greatest common factor(GCF), by the following methods

### Calculate GCF(18,21) by Prime Factorization

Let us represent 18 and 21 as a product of its prime numbers

2 × 3 × 3 is the prime factorization of 18

3 × 7 is the prime factorization of 21

Common factors = 3

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

So, the GCF is 3

### Calculate GCF(18,21) by Listing the Common Factors

Common Factors of 18 and 21: 3

The greatest common factor is 3

The greatest common factor(GCF) or the highest common factor(HCF) of 18 and 21 is 3.