What is the largest number that will divide exactly into 45 and 60?

15 is the GCF (greatest common factor) of 60 and 45.
15x4=60
15x3=45

GCF = 15
for the values 45, 60

Solution by Factorization:
The factors of 45 are: 1, 3, 5, 9, 15, 45

The factors of 60 are: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60

Then the greatest common factor is 15.