One way to find the GCF is to find the prime factorization of each number. So,
25=52
35=5⋅7
Now, we can find all the factors 25 and 35 have in common. We see that 25 and 35 both have a 5, but not 52 because 35 only has one 5.
35 also has a 7, but that is not in the prime factorization of 25, so we do not include it. Since there is only one common factor which is 5, that is our "greatest common factor
