A trader sells 100 articles and earns a profit equal to the selling price of 75 articles. Compute his profit percentage on cost.

Introduction:
When profit is expressed as a multiple of selling price of some quantity, convert it into algebra with per-unit selling price to find cost and then the profit percentage.

Given Data / Assumptions:

• Let s be the selling price per article.
• Total articles sold = 100.
• Profit amount = selling price of 75 articles = 75s.

Concept / Approach:
Total SP = 100s. Cost = SP − Profit. Profit% = Profit / Cost * 100.

Step-by-Step Solution:
Total SP = 100sProfit = 75sTotal Cost = 100s − 75s = 25sProfit% = 75s / 25s * 100 = 300%

Verification / Alternative check:
Numbers: if s = 1, SP = 100, profit = 75, cost = 25 ⇒ 75/25 * 100 = 300%.

Why Other Options Are Wrong:

• 33.33% / 75% / 150%: each uses the wrong base (SP) or misreads the condition.

Common Pitfalls:

• Calculating profit% on selling price rather than on cost price.

Final Answer:
300%