A man buys a watch for Rs. 1950 in cash and sells it for Rs. 2200 at a credit of 1 year. If the rate of interest is 10% per annum, the man:

$$\eqalign{ & {\text{S}}{\text{.P}}{\text{. = P}}{\text{.W}}{\text{.}}\,{\text{of}}\,{\text{Rs}}{\text{.}}\,{\text{2200}}\,{\text{due}}\,{\text{1}}\,{\text{year}}\,{\text{hence}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,\left[ {\frac{{2200 \times 100}}{{100 + \left( {10 \times 1} \right)}}} \right] \cr & \,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,2000 \cr & \therefore {\text{Gain}} = Rs.\left( {2000 - 1950} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = Rs.\,50 \cr} $$