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

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
$$\eqalign{ & = \left( {\frac{{90 - 70}}{{70}}} \right) \times 100 \cr & = \left( {\frac{{20}}{{70}}} \right) \times 100 \cr & = \frac{{200}}{7} \cr & = 28\frac{4}{7}\% \cr} $$