# What is the gcf of 18 24 36?

Find the factors of all three numbers and then find the largest number that is in each list:

i.e. the factors of 18 are 1, 2, 3, 6, 9, 18.

So for example, to find the greatest common factor of 21, 28 and 42, find the factors of each:

Factors of 21 are 1,3,7,21

Factors of 28 are 1,2,4,7,14,28

Factors of 42 are 1,2,3,6,7,14,21,42

The highest number that is in all three lists is 7. Therefore, 7 is the greatest common factor.

Note: A factor is a number that divides evenly into the number. So, 2 divides evenly into 8 so 2 is a factor of 8. 3 divides evenly into 9 so 3 is a factor of 9, etc.

i.e. the factors of 18 are 1, 2, 3, 6, 9, 18.

So for example, to find the greatest common factor of 21, 28 and 42, find the factors of each:

Factors of 21 are 1,3,7,21

Factors of 28 are 1,2,4,7,14,28

Factors of 42 are 1,2,3,6,7,14,21,42

The highest number that is in all three lists is 7. Therefore, 7 is the greatest common factor.

Note: A factor is a number that divides evenly into the number. So, 2 divides evenly into 8 so 2 is a factor of 8. 3 divides evenly into 9 so 3 is a factor of 9, etc.