Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Let's say that I have a tax of 17% over my services and I want to receive $20,000.00 regardless (after paying) the tax.

So I want something like: $$X - 17\% = \$20,000.00$$

Where $X$ is the final value that I need to charge to receive $\$20,000$.

How do I calculate this?

share|cite|improve this question
I think that you wrote this on wrong forum. Questions here should be on research level. – Tomek Tarczynski Dec 16 '10 at 20:25
@Tomek: No, they are not. You are confusing this site with Mathoverflow. Questions of all levels are welcome here. – Aryabhata Dec 16 '10 at 20:26
@Tomek: is for math questions at any level. – Isaac Dec 16 '10 at 20:27
Then sorry, I thought that it is research level forum just as TCS stackexchange. – Tomek Tarczynski Dec 16 '10 at 20:43
up vote 6 down vote accepted

The Rule of Three is your friend.

You want the 83% that is left to be $\$20,000$. If $X$ is 100% of what you need to charge, then you have: $$\begin{array}{rcl} X &\longrightarrow &100\%\\\ 20,000 &\longrightarrow&83\% \end{array}$$ By the Rule of Three, to get the value of $X$ you multiply across the known diagonal and divide by the remaining quantity; so $X = \frac{(20,000)(100)}{83}\approx \$24,096.39$.

share|cite|improve this answer
Thanks! Very clear. – Keyne Viana Dec 16 '10 at 20:58

Removing 17% leaves (100-17)%=83%, so you want 83%*x=20.000. Divide both sides by 83% to get your answer.

share|cite|improve this answer
Thanks. Your answer was very useful. – Keyne Viana Dec 16 '10 at 20:57

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.