The ratio of cost price and selling price of an article is 20 : 21. Then the…

Concept

Profit percent is always measured relative to the cost price, not the selling price. By definition, Profit% = (Selling Price − Cost Price) / Cost Price × 100. When CP and SP are given as a ratio, the ratio numbers themselves can be taken as CP and SP, because the percentage is scale-independent.

Application

1. Let cost price = 20 units and selling price = 21 units (taking the ratio terms directly, since profit% does not depend on the actual scale).

2. Profit = SP − CP = 21 − 20 = 1 unit.

3. Profit% = Profit / CP × 100 = (1 / 20) × 100.

4. (1 / 20) × 100 = 100 / 20 = 5. So profit% = 5%.

Cross-check

Cross-check: 5% of 20 = 1 unit, and 20 + 1 = 21, which matches the given selling price exactly, confirming the result.