Let the cost price (C.P.) of the product be \( x \). We are given that by selling the product for Rs. 1800, the shop owner incurs a loss of 10%.
This implies: \[ Selling Price (S.P.) = 1800 = \left( 1 - \frac{10}{100} \right) \times x = 0.90 \times x \] Thus, \[ x = \frac{1800}{0.90} = 2000 \] So, the cost price of the product is Rs. 2000. Now, to gain a profit of 25%, the shop owner should sell the product for: \[ New Selling Price = \left( 1 + \frac{25}{100} \right) \times 2000 = 1.25 \times 2000 = 2500 \] Thus, the shop owner should sell the product for Rs. 2500 to gain a profit of 25%. To find the selling price for a profit or loss, use the percentage of the cost price corresponding to the profit or loss.