Factoring the GCF of two numbers

Finding the Greatest Common Factor of Two Numbers

Suppose we would like to find the greatest common factor of
18 and 30

First, we factor 18 into its prime factors.
18 = 2 x 3 x 3

Next we factor 30 into its prime factors.
30 = 2 x 3 x 5

What factors do 18 and 30 have in common?