A person buys an article for Rs. p and sells it for Rs. q thereby gaining r% . The selling price in terms of cost price may be written as -

$$\eqalign{ & {\text{C}}{\text{.P}}{\text{.}} = {\text{Rs}}{\text{. p}} \cr & {\text{Gain}} = {\text{r}}\% \cr & \therefore {\text{S}}{\text{.P}}{\text{.}} = {\text{q}} \cr & = \left( {100 + {\text{r}}} \right)\% {\text{ of Rs}}{\text{. p}} \cr & = \frac{{{\text{p}}\left( {100 + {\text{r}}} \right)}}{{100}} \cr} $$