Correct Answer - Option 2 : Rs. 600 and Rs. 400

**Given**

Cost price of two pens = Rs. 10**00**

**Formula used**

Selling Price = Cost price + Profit

Or

Selling price = Cost price - loss

**Calculation**

Let the cost price of one pen is Rs. x and other per is Rs. (1000 - x)

Selling price = x + 10% of x

⇒ 110x/100

Selling price = (1000 - x ) - 15% of (1000 - x)

⇒ (1000 - x) - [15(1000 - x)/100]

⇒ (100000 - 100x - 15000 + 15x)/100

⇒ (85,000 - 85x)/100

There is no loss or profit on selling of pens, therefore cost price is equal to selling price

(85000 - 85x)/100 + 110x/100 = 1000

⇒ 85000 + 25x = 100000

⇒ 25x = 15000

⇒ x = 600

Second 1000 - 600

⇒ Rs. 400

**∴ Cost price of pen is Rs. 600 and Rs. 400**