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 = ?

Answer: Option A

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
$$\begin{array}{rl}& =\text{Rs}.\left(\frac{100}{125}\times 4000\right)\\ & =\text{Rs}.3200\\ & \text{C}\text{.P}\text{. of }{\text{2}}^{\text{nd}}\text{ commodity}\\ & =\text{Rs}\text{.}\left(8000-3200\right)\\ & =\text{Rs}.4800\\ & \text{S}\text{.P}\text{. of }{\text{2}}^{\text{nd}}\text{ commodity}\\ & =\text{Rs}.4000\\ & \therefore \text{loss on }{\text{2}}^{\text{nd}}\text{ commodity}\\ & =\left(\frac{800}{4800}\times 100\right)\%\\ & =16\frac{2}{3}\%\end{array}$$