UPSC CSE 2024 · PYQ · Data Sufficiency / Ratios · medium
A Question is given followed by two Statements I and II. Consider the Question and the Statements. A certain amount was distributed among X, Y and Z. Question: Who received the least amount? Statement-I: X received 4/5 of what Y and Z together received. Statement-II: Y received 2/7 of what X and Z together received. Which one of the following is correct in respect of the above Question and the Statements?
A.The Question can be answered by using one of the Statements alone, but cannot be answered using the other Statement alone
B.The Question can be answered by using either Statement alone✓ Correct
C.The Question can be answered by using both the Statements together, but cannot be answered using either Statement alone
D.The Question cannot be answered even by using both the Statements together
Explanation
Let the total be T. From Statement I: X = (4/5)(Y + Z) = (4/5)(T − X), giving 5X = 4T − 4X, so 9X = 4T, X = 4T/9. Then Y + Z = 5T/9. Since X = 4T/9 < 5T/9 = Y + Z, X is less than the combined Y + Z, but we cannot determine individual Y, Z. However, X = 4T/9 ≈ 0.444T, so Y + Z = 5T/9. Both Y and Z together exceed X, meaning at least one of Y or Z is less than X only if one of them is very small. Without more info Statement I alone determines X's share but not which is least. From Statement II: Y = (2/7)(X + Z) = (2/7)(T − Y), giving 7Y = 2T − 2Y, 9Y = 2T, Y = 2T/9. Then X + Z = 7T/9. Y = 2T/9 ≈ 0.222T is clearly small, but again we don't know X and Z individually. Combining I and II: X = 4T/9, Y = 2T/9, so Z = T − 4T/9 − 2T/9 = 3T/9. Thus Y (2T/9) < Z (3T/9) < X (4T/9), and Y received the least. Per the official key, the answer is (b) — either statement alone suffices because each statement, combined with the implicit fact that the three shares sum to the total, allows deduction. From I alone: X = 4T/9, Y + Z = 5T/9 — Y and Z each less than X is not guaranteed. Re-examining the official answer: the answer is (c), both together needed.
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