2023 CSAT, all questions
UPSC Prelims 2023 · CSAT
Question 55: Logical Reasoning and Mental Ability
What is the middle term of the sequence Z, Z, Y, Y, Y, X, X, X, X, W, W, W, W, W, . . ., A ?
aH
bI
cJ
dM
AnswerUPSC’s answer is (b).
Z appears 2 times, Y 3, X 4, and so on, so the letter at alphabet position p appears 28 - p times, and A appears 27 times. Total terms = 2 + 3 + ... + 27 = 378 - 1 = 377, so the middle term is the 189th. The terms from Z down to I number 2 + 3 + ... + 19 = 190 - 1 = 189. So the 189th term is the last I.
Why each option is right or wrong
- (a) Wrong: H covers the 190th to 209th terms, after the middle.
- (b) Right: the 189th term of 377 is I.
- (c) Wrong: J covers the 153rd to 170th terms, before the middle.
- (d) Wrong: M covers the 105th to 119th terms.
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.