A fruit seller buys lemons at 2 for Re 1 (cost per lemon = Rs 0.50) and sells them at five for Rs 3 (selling price per lemon = Rs 0.60). Compute the gain percentage.

Introduction:
When buying and selling are quoted as pack deals (so many items for a figure), convert to per-unit prices to compare cost and selling price directly. The gain or loss percentage then follows immediately.

Given Data / Assumptions:

• Buy price: 2 for Re 1 ⇒ CP per lemon = Rs 0.50.
• Sell price: 5 for Rs 3 ⇒ SP per lemon = Rs 0.60.

Concept / Approach:
Gain per unit = SP - CP. Gain percentage is gain divided by CP times 100.

Step-by-Step Solution:
CP per lemon = 1 / 2 = Rs 0.50SP per lemon = 3 / 5 = Rs 0.60Gain per lemon = 0.60 - 0.50 = Rs 0.10Gain% = 0.10 / 0.50 * 100 = 20%

Verification / Alternative check:
For 10 lemons: CP = Rs 5, SP = Rs 6, gain = Rs 1, giving 20% on cost. Scaling does not affect the percentage.

Why Other Options Are Wrong:

• 10% and 15%: underestimate from using SP as the base.
• None of these: incorrect because 20% is correct.

Common Pitfalls:

• Confusing per-unit rates when converting from pack prices.

Final Answer:
20%