# Calculate Gross amount when only percent is known

Consider Rs.1000 as my Gross salary and suppose 20% is PF.

so the simple thing is my NET amount is Rs.800.

But when I know only my NET amount i.e. Rs.800 and I know that my 20% PF is already removed. So How can I know my Gross Amount??

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If $X$ is p% of the gross $\mathbf{G}$, then $$X = \frac{p}{100}\mathbf{G}.$$ Solving for $\mathbf{G}$, we have $$\mathbf{G} = \frac{100X}{p}.$$
For example if your net is $1000$, and this is 80% of your gross, then $$\text{Gross} = \frac{100(1000)}{80} = 1250.$$