1. The problem is to find the formula for percentage loss. 2. Percentage loss is calculated when the selling price is less than the cost price. 3. The formula for percentage loss is: $$\text{Percentage Loss} = \left(\frac{\text{Loss}}{\text{Cost Price}}\right) \times 100$$ 4. Where $\text{Loss} = \text{Cost Price} - \text{Selling Price}$. 5. This formula tells us how much percentage of the cost price is lost when an item is sold for less than its cost. 6. Always remember, if the selling price is greater than the cost price, it is a gain, not a loss. 7. Example: If cost price is 200 and selling price is 150, then loss = 200 - 150 = 50. 8. Percentage loss = $\frac{50}{200} \times 100 = 25\%$. 9. So, the percentage loss is 25%.