What is the gcf of 42 and 70.?

The largest number that divides evenly into both 42 and 70 is 7.

To find the GCF, you need to list prime numbers that can multiply into 42 and 70.

42 - 7 * 2 * 3

70 - 7 * 2 * 5

So, the GCF, or Greatest Common Factor, of 42 and 70 is (7 * 2), since you can use the prime numbers 7 and 2 in both of their factor lists.