Getting the Total value from the Nett

Question

I just cant figure out this formula, I thought I will take expert advice to write formula for my php script.

I have a value of $\$80$.

$\$80$ has come from a total sale of $\$100$ and $ 20\%$ is the percentage margin for the respective product.

Now I just have the $\$80$ and want to get the total figure of $\$100$. How can I get the total figure and what would be the formula?

Your help is much appreciated. Thanks in advance

Answer 1

If you mean that you get $80$ from $100$ after a $20$ per cent discount and want to reverse the process, multiply by $\frac{100}{100-20}=\frac{5}{4}$. The formula you need is $y=\frac{5x}{4}$, so if $x=80$, then $y=100$.