How many ways to make 20 with multiplication?

Answer 1

Infinitely many.

Choose any number X such that 0 < X < sqrt(20) and let Y = 20/X.

Then X*Y = X*20/X = 20 and since X was selected arbitrarily, there are infinitely many possible answers to the question.

Answer 2

If you restrict yourself to whole numbers, there are three.

1 x 20

2 x 10

4 x 5