A person bought 50 pens for ₹50 each. He sold 40 of them at a loss of 5%. He wants to gain 10% on the whole. Then his gain percent on the remaining pens should be:

170%

Price of 50 pens = Rs.50

Price of 40 pen = Rs.40

ATQ,

S.P. 40 pen @5% loss = Rs.38

To earn 10% profit on all pens,

S.P. should be Rs.55 (i.e. 110% of 50)

Now profit is to be earn on remaining 10 pens = Rs. 17

Therefore,

gain % on the remaining 10 pens =  \(\frac{17}{10}\) × 100 = 170%