1. **Problem:** A trader sold a wrist watch for 3150 after giving a 10% discount. Find the marked price of the watch. 2. **Formula:** The selling price (SP) after discount is related to the marked price (MP) by the formula: $$ SP = MP \times (1 - \text{discount rate}) $$ where the discount rate is expressed as a decimal. 3. **Given:** - Selling price, $SP = 3150$ - Discount rate = 10% = 0.10 4. **Substitute values:** $$ 3150 = MP \times (1 - 0.10) $$ $$ 3150 = MP \times 0.90 $$ 5. **Solve for MP:** $$ MP = \frac{3150}{0.90} $$ $$ MP = 3500 $$ 6. **Answer:** The marked price of the watch is 3500. This means the watch was originally priced at 3500 before the 10% discount was applied to sell it at 3150.