If selling price is doubled, the profit triples. Find the profit percent.

$$\eqalign{ & {\text{Let}}\,{\text{C}}{\text{.P}}{\text{.}}\,{\text{be}}\,{\text{Rs}}{\text{.}}\,x\,{\text{and}}\,{\text{S}}{\text{.P}}{\text{.}}\,{\text{be}}\,{\text{Rs}}.\,y \cr & {\text{Then}},\,3\left( {y - x} \right) = \left( {2y - x} \right) \cr & \Rightarrow y = 2x \cr & {\text{Profit}} = Rs.\,\left( {y - x} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,\left( {2x - x} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,x \cr & \therefore {\text{Profit}}\,\% \cr & = \left( {\frac{x}{x} \times 100} \right)\% \cr & = 100\% \cr} $$