A person purchased 10 dozen pens at the rate of Rs. 4 per dozen. On checking, he found that 20 pens were not working. In order to earn 25% profit, he should sell the remaining pens each at -

Answer: Option C

Total C.P. of (10 × 12) i.e.,
120 pens = Rs. (4 × 10) = Rs. 40
Number of working pens
= (120 - 20) = 100
Total selling price of 100 pens
$$\begin{array}{rl}& =\text{Rs}\text{.}\left(\frac{125}{100}\times 40\right)\\ & =\text{Rs}\text{. }50.\\ & \therefore \text{S}\text{.P}\text{.of each pen}\\ & =\text{Rs}.\left(\frac{50}{100}\right)\\ & =\text{50 paise}\end{array}$$