Profit and Loss — A fruit-seller buys lemons at 2 for ₹ 1 (CP per lemon = ₹ 0.50) and sells them at 5 for ₹ 3 (SP per lemon = ₹ 0.60). Compute the gain percentage.

Introduction / Context:
Unitary-method profit questions compare cost per unit with selling price per unit. Once per-unit values are known, profit% = (SP − CP)/CP * 100.

Given Data / Assumptions:

• Buying rate: 2 lemons for ₹ 1 ⇒ CP per lemon = ₹ 0.50
• Selling rate: 5 lemons for ₹ 3 ⇒ SP per lemon = ₹ 0.60

Concept / Approach:
Compute the per-unit profit and express it as a percentage of the CP. This avoids fractions across different bundle sizes.

Step-by-Step Solution:

Verification / Alternative check:
On any multiple of lemons, the ratio SP/CP per unit remains the same, so the calculated percentage holds for the full lot as well.

Why Other Options Are Wrong:
10% and 15% undervalue the profit; 25% overstates it. Only 20% matches the computed (SP − CP)/CP * 100.

Common Pitfalls:
Mixing the bundle sizes without first converting to per-unit prices often leads to wrong ratios.

Final Answer:
20%