UPSC Prelims 2022 · CSAT
Question 30: Logical Reasoning and Mental Ability
Three persons A, B and C are standing in a queue not necessarily in the same order. There are 4 persons between A and B, and 7 persons between B and C. If there are 11 persons ahead of C and 13 behind A, what could be the minimum number of persons in the queue?
AnswerUPSC’s answer is (a).
Number the places from the front. C has 11 ahead, so C is 12th. With 7 between B and C, B is 4th or 20th. With 4 between A and B, A is 5 places from B: for B = 4, A = 9; for B = 20, A = 15 or 25. A has 13 behind, so the total is A's place plus 13: 22, 28 or 38. The minimum is 22 (check: places 4, 9 and 12 leave 4 persons between A and B and 7 between B and C).
Why each option is right or wrong
- (a) Correct: B 4th, A 9th, C 12th, with 13 behind A, gives 22.
- (b) 28 is possible (A 15th, B 20th) but not the minimum.
- (c) 32 does not arise from any arrangement.
- (d) 38 is possible (A 25th) but not the minimum.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2022, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.