What is the greatest common factor of 20 and 36?

The factors of 20 include 1, 2, 4, 5, 10, and 20. The factors of 36 include 1, 2, 3, 4, 6, 9, 12, 18, and 36. Their greatest shared factor is 4, so the answer is 4.

AI-written and checked against the verified answer.