Apples are bought at 5 for Rs. 50 and an equal number at 10 for Rs. 50. They are mixed and sold at 6 for Rs. 50 the gain percent is

Take n apples bought at 5 for Rs 50, so each costs Rs 10, giving Rs 10n. Take another n bought at 10 for Rs 50, so each costs Rs 5, giving Rs 5n. Total cost is Rs 15n for 2n apples.

Selling 6 for Rs 50 means each apple fetches Rs 50/6, so 2n apples bring in 2n × 50/6 = Rs 50n/3, about Rs 16.67n.

Profit = 50n/3 − 15n = 5n/3. Gain % = (5n/3) ÷ 15n × 100 = 11.11%.

• A) 20 is wrong. It comes from using the wrong average cost, such as taking the simple average of the two buying prices as the cost of each apple.
• B and C are blank in this version of the paper, so they cannot be treated as valid choices.
• D) None of the above is correct because 11.11% matches none of the given values.

Core concept: weighted average cost in mixture problems, where equal quantities bought at different rates must be costed as a total, not averaged per rate. This also feeds into the Quantitative Aptitude and reasoning sections, and the same method works for any blend-and-sell question.

Trap: averaging the two rates (7.5 per apple) and then computing gain on that is close but leads you to the wrong percentage, which tempts you into picking A.