Okay ....
Lets say you got a discount of 20% on a 40 dollar bike ....
To get the answer of how much off the bike is multiple 40 and 20%
In math if you are about to multiply a percent to a whole number put a decimal in front of it.
Example : 
.20 × 40 = 8 
So the bike is 8 dollars off 
If you want to find the new price after the discount just subtract the answer ( 8 ) 
40 ( the original price ) - 8 ( the discount total ) 
The answer would be 32
The new price for the bike adding the discount would be $32.oo