A shopkeeper expects a gain of 22.5% on his cost price. If in a week, his sale was of Rs. 392, what was his profit?

$$\eqalign{ & {\text{C}}{\text{.P}}{\text{.}}\, = \,Rs.\,\left( {\frac{{100}}{{122.5}} \times 392} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,Rs.\,\left( {\frac{{1000}}{{1225}} \times 392} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,320 \cr & \therefore {\text{Profit}} = Rs.\,\left( {392 - 320} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,72 \cr} $$