Mathematically we want to split it up into 100 parts that are equal. Then count 40 out of it. We will use 300 as in we had 300 mnm's or something. For that you would select 40 or in other words 40 * 3 = 120.
[tex] \frac{40}{100} * 300 = 120 \ \textgreater \ \frac{40/20}{100/20} = \frac{2}{5} [/tex]
