Question

13 is 25% of what number

Answer 1

Hack way
25%=1/4
13 is 1/4 of something
1/4 times 4=4/4=1

therefor
13 times 4=1 whole
13*4=52
the original number is 52

Answer 2

13 is 25% of the number 52.
13/25%(or .25) = 52 >>> 13/0.25 = 52
I divided because if you multiply, you get 3.25, which isn't what your looking for. :D