UPSC Prelims 2026 · CSAT
Question 57: Logical Reasoning and Mental Ability
In a sequence of numbers, each number other than the first two is the sum of the two immediately preceding numbers from it. If the first two numbers in the sequence are 4 and 7, then the sixth number is
AnswerUPSC’s answer is (d).
Each term after the first two is the sum of the two before it: first 4, second 7, third 4 + 7 = 11, fourth 7 + 11 = 18, fifth 11 + 18 = 29, sixth 18 + 29 = 47. The option 29 is the fifth term, and neither 37 nor 43 appears in this sequence at all.
Why each option is right or wrong
- (a) Wrong: 29 is the fifth term.
- (b) Wrong: 37 is not in the sequence.
- (c) Wrong: 43 is not in the sequence.
- (d) Right: 18 + 29 = 47.
Only the provisional key (27 May 2026) was found; the final key replaces it when found.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2026, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.