UPSC Prelims 2023 · CSAT
Question 38: Logical Reasoning and Mental Ability
Consider the following statements :
- 1.A is older than B.
- 2.C and D are of the same age.
- 3.E is the youngest.
- 4.F is younger than D.
- 5.F is older than A.
How many statements given above are required to determine the oldest person/persons ?
AnswerUPSC’s answer is (d).
Build the order. Statement 4: D is older than F. Statement 5: F is older than A. Statement 1: A is older than B. Statement 2: C and D are the same age. So C = D > F > A > B. Statement 3 places E below everyone. Drop any one statement and a rival for oldest remains: C, F, A, B or E, depending on which is dropped. So all five statements are needed to name the oldest persons, C and D.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: dropping any statement leaves a rival for oldest.
- (b) Wrong: dropping any statement leaves a rival for oldest.
- (c) Wrong: dropping any statement leaves a rival for oldest.
- (d) Right: each statement removes one possible rival, so all five are required.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2023, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.