What is the greatest common factor of 40 and 20?

Answer 1

To find the greatest common factor, list the prime factors of each number:

40: 2 x 2 x 2 x 5

20: 2 x 2 x 5

Then select the factors that each share:

2 x 2 x 5 (they each share these individual numbers)

So, the greatest common factor is 20.
Since 20 is a factor of 40, it is automatically the GCF.

Answer 2

Factors of 20: 1 2 4 5 10 20 Factors of 40: 1 2 4 5 8 10 20 40 The GCF of 20 and 40 is 20