Answer
The statement is true because it is really 20 is the Greatest Common Factor of 40, 80 and 100.
Work Step by Step
The factors of 40 are {1, 2, 4, 5, 8, 10, 20, 40}, the factors of 80 are {1, 2, 4, 8, 10, 20, 40, 80}, and the factors of 100 are {1, 2, 4, 5, 10, 20, 25, 50, 100}. The greatest common number in those sets is 20. Therefore, the Greatest Common Factor is 20.
