What is the gcf of 20 and 30?

The greatest common factor (GCF) of 20 and 30 is 10. This is because 10 is the largest number that can evenly divide both 20 and 30 without leaving a remainder. The factors of 20 are 1, 2, 4, 5, 10, and 20, while the factors of 30 are 1, 2, 3, 5, 6, 10, 15, and 30. The GCF is therefore the largest number that appears in both lists, which in this case is 10.