UPSC Prelims 2013 · CSAT
Question 12: Logical Reasoning and Mental Ability
If a person visits each of the places starting from P and gets back to P, which of the following places must he visit twice ?
AnswerUPSC’s answer is (b).
Treat the cities as points and the links as lines: P-Q, Q-T, T-R and R-P make a loop, while S hangs off R alone. A round trip from P that visits every city must go out to S and come back, and S can be entered and left only through R. So R is passed through twice, for example P-Q-T-R-S-R-P. Q, T and S each need just one visit. A dead-end branch always forces a repeat of the city where it joins the network.
Why each option is right or wrong
- (a) Wrong. Q lies on the loop and is visited once.
- (b) Right. S is a dead end reached only through R, so R is visited twice.
- (c) Wrong. S is a dead end, visited once.
- (d) Wrong. T lies on the loop and is visited once.
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.