Mixing equal quantities at different costs: Two lots of onions of equal weight are mixed—one costing ₹ 10 per kg and the other ₹ 15 per kg. The entire mixture is sold at ₹ 15 per kg. Compute the percentage profit or loss.

Introduction / Context:
When equal quantities are mixed, the average cost per kg is the simple average of the two rates. Compare the selling price per kg to this average cost to determine profit%.

Given Data / Assumptions:

• Equal-weight lots at ₹ 10/kg and ₹ 15/kg.
• Mixture sold at ₹ 15/kg.

Concept / Approach:
Average cost per kg = (10 + 15)/2 = ₹ 12.50. Profit% = (SP − AvgCost)/AvgCost * 100.

Step-by-Step Solution:
Average cost = ₹ 12.50 per kgSelling price = ₹ 15 per kgProfit per kg = 15 − 12.50 = ₹ 2.50Profit% = 2.50 / 12.50 * 100 = 20%

Verification / Alternative check:
Take 1 kg from each lot (total 2 kg). Total cost = 10 + 15 = ₹ 25. Revenue = 2 * 15 = ₹ 30. Profit = ₹ 5 = 20% of ₹ 25—confirms the calculation.

Why Other Options Are Wrong:

• 10% profit: too low; average cost is ₹ 12.50 not ₹ 13.50.
• 10% loss / 20% loss: sign is incorrect since SP exceeds average cost.

Common Pitfalls:

• Using a weighted average other than 50:50; the problem states equal quantities.

Final Answer:
20% profit