UPSC Prelims 2017·CSAT·Logical Reasoning·Arrangement and Puzzles

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. While travelling from C to H, which one of the following stations must be passed through?

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Last updated 23 May 2026, 3:31 pm IST
  1. AG
  2. BECorrect
  3. CB
  4. DF

Explanation

To travel from C to H, we must trace the possible paths: 1. From C, the only outgoing passage is C -> A. Therefore, A must be passed through. 2. From A, the only passage that progresses towards H (and not back to C) is A -> E (due to the two-way passage A E). Therefore, E must be passed through after A. At this point, we have established that any path from C to H must start with C -> A -> E. Let's explore paths from E to H: Path 1: C -> A -> E -> D -> H (using E D and D -> H) Path 2: C -> A -> E -> G -> B -> F -> D -> H (using E -> G, G B, B -> F, F D, D -> H) In both identified paths from C to H, the station E is passed through. Since E is an unavoidable station on any route from C to H, it must be passed through. Let's check the other options: A) G: Path 1 (C -> A -> E -> D -> H) does not pass through G. So G is not mandatory. C) B: Path 1 (C -> A -> E -> D -> H) does not pass through B. So B is not mandatory. D) F: Path 1 (C -> A -> E -> D -> H) does not pass through F. So F is not mandatory. Therefore, E is the only station among the options that must be passed through. The final answer is B) E.
Logical Reasoning: Eight railway stations A, B, C, D, E, F, G and H are connected either by two- way passages or one- way passages. One- wa
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