The GCF of 24 and 90 is 6. The factors of 24 are 1, 2, 3, 4, 6, 8, 12, and 24. The factors of 90 are 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, and 90. The common factors are 1, 2, 3, and 6, so the greatest common factor is 6. You can also determine the greatest common factor using the prime factors.