Common factors of 40 36

So,

I'm not sure if you are looking for simply common factors or the greatest common factor.

Factors of 40: 1, 2, 4, 5, 8, 10, 20, 40

Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36

The common factors are 1, 2, and 4.

But the greatest of these (GCF) is 4.

The factors of 36 are:

1, 2, 3, 4, 6, 9, 12, 18, 36

The factors of 40 are:

1, 2, 4, 5, 8, 10, 20, 40

The common factors are:

1, 2, 4