What is the gcf of 15 and 20?

The GCF (Greatest Common Factor) of 15 and 20 is 5. This means that 5 is the largest factor that both 15 and 20 have in common without any remainders. The factors of 15 are 1, 3, 5, and 15, while the factors of 20 are 1, 2, 4, 5, 10, and 20. The only number that appears in both lists is 5, which is therefore the GCF.