What is the greatest common factor of 180 and 225?
Let's do a prime factorization of the two numbers:
And now let's find what's in the GCF by seeing what is common to both:
There are 2s in 180 but not 225, so there are no 2's in the GCF.
There are two 3s in both 180 and 225, and so the GCF has two 3s.
There is one 5 in 180 and two in 225, and so the GCF has one 5.
And now let's put it all together: