What is the greatest common factor of 18 and 21?

Answer 1

The greatest common factor (GCF) of two numbers is the largest number that divides both numbers without leaving a remainder. To find the GCF of 18 and 21, you can list the factors of each number: 18 (1, 2, 3, 6, 9, 18) and 21 (1, 3, 7, 21). The common factors are 1 and 3, and the greatest common factor is 3.

Answer 2

The GCF of 18 and 21 is 3.

The prime factorization of 18 is 2*3*3

The prime factorization of 21 is 3*7

So the GCF of 18 and 21 is 3.

You can also notice that the difference between 21 and 18 is 3. The GCF can be no larger than the difference between the numbers. Since 3 is a factor of both 18 and 21, it is the GCF.
The GCF is 3.
3

Answer 3

3.

Answer 4

3