A book seller allowed 10% discount on printed price. He gets 30% commission from publisher. His profit in percent will be?

Answer: Option B

Let the marked price be of book be Rs. 100
Cost price of the retailer = Rs. (100 - 30) = Rs. 70
Selling price for the retailer = Rs. 90
∴ Profit percent
$$\begin{array}{rl}& =\left(\frac{90-70}{70}\right)\times 100\\ & =\left(\frac{20}{70}\right)\times 100\\ & =\frac{200}{7}\\ & =28\frac{4}{7}\%\end{array}$$