What is the greatest common factor for 28 and 66?

The factors of 28 are: 1, 2, 4, 7, 14, 28.

The factors of 66 are: 1, 2, 3, 6, 11, 22, 33, 66.

The common factors are: 1, 2.

The Greatest Common Factor (GCF) is: 2