A shopkeeper sells one transistor for Rs. 840 at a gain of 20% and another for Rs. 960 at a loss of 4%. His total gain or loss percent is:

$$\eqalign{ & {\text{C}}{\text{.P}}{\text{.}}\,{\text{of}}\,{1^{st}}\,{\text{transistor}} \cr & = Rs.\,\left( {\frac{{100}}{{120}} \times 840} \right) = Rs.\,700 \cr & {\text{C}}{\text{.P}}{\text{.}}\,{\text{of}}\,{2^{nd}}\,{\text{transistor}} \cr & = Rs.\,\left( {\frac{{100}}{{96}} \times 960} \right) = Rs.\,1000 \cr & {\text{So,}}\,{\text{total}}\,{\text{C}}{\text{.P}}{\text{.}}\, = Rs.\,\left( {700 + 1000} \right) = Rs.\,1700 \cr & {\text{Total}}\,{\text{S}}{\text{.P}}{\text{.}}\, = \,Rs.\,\left( {840 + 960} \right) = Rs.\,1800 \cr & \therefore {\text{Gain}}\,\% = \left( {\frac{{100}}{{1700}} \times 100} \right)\% = 5\frac{{15}}{{17}}\% \cr} $$