A man sells two commodities for Rs. 4000 each, neither losing nor gaining in the deal. If he sold one commodity at a gain of 25%, the other commodity is sold at a loss of = ?

Total S.P. = Rs. 8000 and
Total C.P. = Rs. 8000
S.P. of 1^st commodity = Rs. 4000
Gain on it = 25%
∴ C.P. of 1^st commodity
$$\eqalign{ & = {\text{Rs}}.\left( {\frac{{100}}{{125}} \times 4000} \right) \cr & = {\text{Rs}}.3200 \cr & {\text{C}}{\text{.P}}{\text{. of }}{{\text{2}}^{{\text{nd}}}}{\text{ commodity}} \cr & = {\text{Rs}}{\text{.}}\left( {8000 - 3200} \right) \cr & = {\text{Rs}}.4800 \cr & {\text{S}}{\text{.P}}{\text{. of }}{{\text{2}}^{{\text{nd}}}}{\text{ commodity}} \cr & = {\text{Rs}}.4000 \cr & \therefore {\text{loss on }}{{\text{2}}^{{\text{nd}}}}{\text{ commodity}} \cr & = \left( {\frac{{800}}{{4800}} \times 100} \right)\% \cr & = 16\frac{2}{3}\% \cr} $$