Oranges are bought at 5 for Rs. 10 and sold at 6 for Rs. 15. The gain percentage is = ?

Answer: Option D

Let the (LCM of 5 and 6 = 30) oranges be bought.
$$\begin{array}{rl}& \therefore \text{CP of 30 oranges}\\ & =\frac{10}{5}\times \text{30}\\ & =\text{Rs}\text{. 60}\\ & \text{Their Selling price}\\ & =\frac{15}{6}\times 30\\ & =\text{Rs}\text{. 75}\\ & \text{Profit}=\text{Rs}\text{.}\left(\text{75}-\text{60}\right)\\ & =\text{Rs}\text{. 15}\\ & \therefore \text{Profit percent}\\ & =\left(\frac{15}{60}\right)\times 100\\ & =25\%\end{array}$$