The great common factor of 9 and 15 is 3
That is because if you look at the factors of 9 and 15, you would see that they only have 1, and 3 that are alike.
Since 3 is larger than 1, 3 is the greatest common factor
Write the factors (parts) of both
9 = 1, 3, 9
15 = 1 3 5 15
What is the the greats factor they have in common? 3
GCF is 3
