UPSC Prelims 2017 · CSAT
Question 78: Logical Reasoning and Mental Ability
Eight railway stations A, B, C, D, E, F, G and H are connected either by two-way passages or one-way passages. One-way passages are from C to A, E to G, B to F, D to H, G to C, E to C and H to G. Two-way passages are between A and E, G and B, F and D, and E and D. If the route between G and C is closed, which one of the following stations need not be passed through while travelling from H to C?
AnswerUPSC’s answer is (c).
With the G to C road closed, H's only exit is H to G. From G the road goes to B, then B to F, F to D, D to E, and E to C. The route is H, G, B, F, D, E, C. Station A is never needed, because E reaches C directly. So A need not be passed through, while E, D and B must be.
Why each option is right or wrong
- (a) E is needed: the only remaining way into C is E to C.
- (b) D is needed to get from F to E.
- (c) Correct: E goes straight to C, so A is not on the route.
- (d) B is needed to leave G once the G to C road is closed.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2017, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.