Question

What times what equals 400

Answer 1

If you're willing to consider fractions or decimals,
then there are an infinite number of answers. 
Like (2.5 x 160), and (15 x 26-2/3).

If you want to stick to only whole numbers,
then these 8 combinations do:

1, 400
2, 200
4, 100
5, 80
8, 50
10, 40
16, 25
20, 20