# Thread: Silly Problem I cant figure out with percentage

1. ## Silly Problem I cant figure out with percentage

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?

2. ## Re: Silly Problem I cant figure out with percentage

Hey bjbauer.

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.

3. ## Re: Silly Problem I cant figure out with percentage

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 $\displaystyle \frac{130}{100}= \frac{13}{10}$. To go back use the reciprocal, $\displaystyle \frac{10}{13}$. You can calculate that $\displaystyle \frac{10}{13}= 0.769$, approximately, which you can write as 76.9%.