UPSC Prelims 2020 · CSAT
Question 34: Logical Reasoning and Mental Ability
Consider the following sequence of numbers : 5 1 4 7 3 9 8 5 7 2 6 3 1 5 8 6 3 8 5 2 2 4 3 4 9 6 How many odd numbers are followed by the odd number in the above sequence?
AnswerUPSC’s answer is (b).
Mark each odd number followed immediately by another odd number: 5-1, 7-3, 3-9, 5-7, 3-1 and 1-5. Every other odd number is followed by an even number. Reading the two printed lines as one continuous sequence adds nothing, because the last number of the first line, 5, is followed by 8. The count is 6.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Misses one pair: there are six, not five.
- (b) Right: there are six such pairs.
- (c) Overcounts: only six pairs exist.
- (d) Overcounts by two.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.