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.**