I have 12.00 item for sale i want to mark up 30% that would be 3.60 + 12.00 = 15.60
now what calculation do i do to get back to 12.00?
If i have 15.60 and i know i started at 12 how do i get the 3.60?
If you added 30%, your new value is 100% + 30% = 130% of the original.
So algebraically you have new = old * 130% = old * 1.3.
So if you have new and what to get old, we re-arrange to get
new/(1.3) = old and since 1.3 = 13/10, we get
new/(13/10) = (new*10)/13 = old.
Just to add a little bit to what chiro said, since you added 30% to the whole, that is a total of 100%+ 30%= 130% as chiro said. That can be written as . To go back use the reciprocal, . You can calculate that , approximately, which you can write as 76.9%.