Correct Answer - Option 1 : 35%

**Given: **

Cost price of 6 pens = Rs. 20

The selling price of 4 pens = Rs. 18

**FormulaUsed:**

Cost price = Selling price - Profit

Profit% = (Profit/Cost price) × 100

**Calculation:**

Cost price of 6 pens = Rs. 20

⇒ Cost price of 1 pen = 20/6 = 10/3

The selling price of 4 pens = Rs. 18

⇒ The selling price of 1 pen = 18/4 = 9/2

⇒ Profit = 9/2 - 10/3 = 7/6

Profit% = (Profit/Cost price) × 100

⇒ Profit% = \(\frac{\frac{7}{6}}{\frac{10}{3}} \times 100\)

∴ Profit% = 35%

The correct option is 1 i.e. 35%