Explanation:

- The dealer purchased the washing machine for Rs 9,000.

- The dealer wants a gain of 10% on the cost price.

- This means the selling price needs to be: Rs 9,000 + 10% of Rs 9,000 = Rs 9,900.

- He offers a discount of 10% on the marked price.

- So, the marked price multiplied by 90% (or 0.9) should equal the selling price (Rs 9,900).

To find the marked price, use the equation:

$$\text{Marked Price}\times 0.9=9,900$$

Solving for the marked price, you get:

$$\text{Marked Price}=\frac{9,900}{0.9}=Rs11,000$$

- Option 1: Rs 11,000 is correct.

- Option 2: Rs 12,000 is incorrect.

- Option 3: Rs 13,000 is incorrect.

- Option 4: Rs 10,000 is incorrect.