How to calculate percentage of a percentage

srsly, I can't understand it. can someone help me by giving a step by step procedure on how to solve a problem? Desperately, I'm in need of it.

say you are asked to calculate 25% of 40% of 2500
first we calculate 40% of 2500
this is 40/100 * 2500 = 1000

now we calculate 25% of 1000
25/100 * 1000 = 250
so 25% of 40% of 2500 = 250

NOTE the order i followed, first 40 then 25
its always inside to outside!!!

Basically to calculate a percentage of a percentage is to look at them as decimals or fractions. For example, 50% of 50%=.5*.5=1/2 * 1/2 = .25=1/4.