Correct Answer - Option 2 : 130
Given
Shopkeeper pay per pen is Rs 10
Formula used
Profit = SP – CP,
Profit % = Profit/CP × 100,
Where,
SP is selling price,
CP is cost price,
Calculation
We have profit % = 100%,
⇒ 100 = (10 – CP/CP) × 100
⇒ CP = 10 – CP
⇒ 2CP = 10
⇒ CP = Rs. 5
Profit = 10 – 5 = Rs. 5
So he earns profit of Rs. 5 on one pen.
To gain Rs. 650,
⇒ 650/5 = 130
∴ He should sell 130 pens to gain profit of Rs. 650.