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UPSC Prelims 2025 CSAT, question 8

Topic: Series and patterns

Q8

What comes at XX and YY respectively in the following sequence ?

January, January, December, October, XX, March, October, YY, September

  1. (a) July, May
  2. (b) July, AprilCorrect answer
  3. (c) June, May
  4. (d) June, April

Solution.

Answer: (b) July, April

  1. Representing the months by their calendar numbers (Jan=1,Feb=2,…,Dec=12\text{Jan} = 1, \text{Feb} = 2, \dots, \text{Dec} = 12), the sequence moves backward by 0,1,2,3,4,5,6,70, 1, 2, 3, 4, 5, 6, 7 months at successive steps.
  2. Starting at January (11): 1−0=11 - 0 = 1 (January); 1−1≡121 - 1 \equiv 12 (December); 12−2=1012 - 2 = 10 (October); 10−3=710 - 3 = 7 (July =X= X); 7−4=37 - 4 = 3 (March).
  3. Continuing from March (33): 3−5≡103 - 5 \equiv 10 (October); 10−6=410 - 6 = 4 (April =Y= Y); and 4−7≡94 - 7 \equiv 9 (September), so XX and YY are July and April.