A man purchased 150 pens at the rate of Rs. 12 per pen. He sold 50 pens at a gain of 10%. The percentage gain at which he must sell the remaining pens so as to gain 15% on the whole outlay is = ?

Explanation:-

According to the question,
Pen × Profit (%) = Total Profit
Total 150 pens × 15 = 2250
50 × 10 = 500
100 × a = 1750
a = 17.5
∴ Remaining profit % of pen = 17.5%