What is the greatest common factor of 198 and 220?

The GCF of 198 and 220 is 22.

The factors of 198 are 1, 2, 3, 6, 9, 11, 18, 22, 33, 66, 99, and 198.

The factors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110, and 220.

Therefore, the greatest common factor of 198 and 220 is 22.

Another way to determine this is to determine the prime factors of each.

The prime factors of 198 are 2, 3, 3, and 11.

The prime factors of 220 are 2, 2, 5, and 11.

The factors they have in common are one 2 and the 11, so their greatest common factor is the product 2 x 11 = 22.