Correct Answer - Option 4 : 25%

**Given**

Cost price of 10 mobiles = Selling price of 8 mobiles

**Formula used**

Gain % = (Gain/Cost price) × 100

**Calculation**

Cost price of 10 mobiles = Rs. 1,00,000

Cost price of 1 mobile = Rs. 10,000

Selling Price of 8 mobiles = Rs. 1,00,000

Selling price of 1 mobile = Rs. 12,500

Profit on 1 mobile = Rs. 12,500 - Rs. 10,000

⇒ Rs. 2,500

Profit % = (2500/10,000) × 100

⇒ 25%

**∴ Gain percent is 25%**