UPSC Prelims 2013 · CSAT
Question 19: Logical Reasoning and Mental Ability
Five people A, B, C, D and E are seated about a round table. Every chair is spaced equidistant from adjacent chairs. (i) C is seated next to A. (ii) A is seated two seats from D. (iii) B is not seated next to A. Which of the following must be true ?
- ID is seated next to B.
- IIE is seated next to A.
Select the correct answer from the codes given below :
AnswerUPSC’s answer is (c).
Put A at seat 0 of a circle of five seats. Seats 1 and 4 are next to A; seats 2 and 3 are two seats away. D is two seats from A, so D is at seat 2 (or seat 3, the mirror case). B is not next to A, so B cannot be at seat 1 or 4, and the only free seat among 2 and 3 is the other one. That makes D and B neighbours. C and E fill seats 1 and 4, and both are next to A. So both I and II must be true.
- I. D and B must take the two seats far from A, which are adjacent.
- II. C and E fill the two seats beside A.
How you could have got this
- If you were sure statement I is correct, (b) and (d) go: each of them leaves I out.
What you needed to know: D and B must take the two seats far from A, which are adjacent.
- Then, if you were sure statement II is correct, (a) goes: it leaves II out.
What you needed to know: C and E fill the two seats beside A.
Only (c) is left. This one needs every statement.
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) Wrong. II is also true: E is next to A.
- (b) Wrong. I is also true: D is next to B.
- (c) Right. D sits next to B, and E sits next to A.
- (d) Wrong. Both statements hold.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.