What are all the common factors of 20 and 50

The factors of 20 are 1, 2, 4, 5, 10, and 20.

The factors of 50 are 1, 2, 5, 10, 25, and 50.

When we look at both lists, to find the numbers that are on both lists,

we see that the common factors of 20 and 50 are ...

1, 2, 5, and 10.