A person bought 60 books for ₹60 each. He sold 50 of them at a loss of 4%. At what percent profit should he sell the remaining books so that he gains 5% in the entire transaction?

50%

Let the Cost price of 60 books is = Rs.60 

50 of them is sold at a loss of 4% so the selling price of 50 = 50 × \(\frac{96}{100}\) = 48

He wants to gain 5% on entire transaction so the selling price of entire books should be = 105% of 6 = 63

So he should sell the remaining at = 63 - 48 = 15 rupees.

So the profit on remaining = (15 - 10) × \(\frac{100}{10}\) = 50%