What are the common factors of 160 and 200?

Factors of 160 are 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 80, 160.

Factors of 200 are 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 200.

Not counting 1, the common factors are 2, 4, 5, 8, 10, 20, 40.

[Note that 1 and the number itself are not usually counted as factors.]