128/640 is 0.2 so 128/640 is 20%.

You can cross multiply to find the answer like so:

128/640 = x/100

100*128/640= x

12800/640=x

20=x

Or you could divide 640 by 6.4 because you know that it will give you 100 and then divide 128 by 6.4 also which would give you 20.

You can cross multiply to find the answer like so:

128/640 = x/100

100*128/640= x

12800/640=x

20=x

Or you could divide 640 by 6.4 because you know that it will give you 100 and then divide 128 by 6.4 also which would give you 20.