A person bought 50 pens for Rs. 50. 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 = ?

Explanation:-

According to the question,
Cost price of pen = Rs. 50
Cost price of 50 pen = Rs. 50 × 50
=Rs. 2500
To gain 10% overall sold at = Rs. 2750
Now, 40 pen sold at 5% loss
∴ Selling price of 4 pens
= 40 × 47.5
= Rs. 1900
Remaining 10 pens sold to get overall profit of 10% at selling price of 1 (remaining pens) $$= \frac{{850}}{{10}} = {\text{Rs}}{\text{. 85}}$$ Cost price of 1 pen = Rs. 50
Profit % of remaining pens $$\eqalign{ & {\text{ = }}\frac{{35}}{{50}} \times 100 \cr & = 70\% \cr}$$