To solve this problem, we need to understand the scenario: The shopkeeper claims to sell rice at cost price but uses a false weight to gain profit. Furthermore, the customer accidentally pays 10% less than expected.
First, let's determine how the shopkeeper achieves a 25% profit through the use of a false weight.
- Suppose the actual weight of rice he should give is 1000 grams (or 1 kg), and let the cost price of 1 kg be \(C\).
- To aim for a 25% profit, the shopkeeper should sell less quantity while he still gets the money equivalent to 1 kg.
- If he uses \(x\) grams as the weight, then he sets up his selling condition as: \(x = \frac{1000}{1 + \frac{25}{100}}\).
- This simplifies to: \(x = \frac{1000}{1.25} = 800\) grams.
- Thus, he uses a weight of 800 grams instead of 1000 grams while claiming to sell at cost price.
Now, to calculate the profit after the customer pays 10% less:
- The customer should pay \(C\), but actually pays \(0.9C\).
- Therefore, selling 800 grams for \(0.9C\) gives the actual selling price for 1000 grams as: \(\frac{0.9C}{800} \times 1000 = 1.125C\).
- Thus, selling price per kg turns out to be 1.125 times the cost price which implies a profit percentage of: \(= 12.5\%\).
Hence, the actual profit percentage made by the shopkeeper is 12.5%, which corresponds to the correct option.