2022 CSAT, all questions
UPSC Prelims 2022 · CSAT
Question 4: Logical Reasoning and Mental Ability
What is the value of X in the sequence 20, 10, 10, 15, 30, 75, X?
a105
b120
c150
d225
AnswerUPSC’s answer is (d).
Look at the ratio of each term to the one before it: 10/20 = 1/2, 10/10 = 1, 15/10 = 3/2, 30/15 = 2, 75/30 = 5/2. The multipliers rise by 1/2 each step: 1/2, 1, 3/2, 2, 5/2, so the next multiplier is 3. X = 75 × 3 = 225. For sequences that first fall and then rise, test ratios before differences: the differences here (−10, 0, 5, 15, 45) show no clean rule, while the ratios do.
Why each option is right or wrong
- (a) 105 adds 30 to 75, which breaks the pattern of multipliers rising by 1/2.
- (b) 120 would need a multiplier of 1.6, not 3.
- (c) 150 would need a multiplier of 2, which repeats an earlier step.
- (d) Correct: 75 × 3 = 225.
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.