2015 CSAT, all questions

UPSC Prelims 2015 · CSAT

Question 33: Logical Reasoning and Mental Ability

Shahid and Rohit start from the same point in opposite directions. After each 1 km, Shahid always turns left and Rohit always turns right. Which of the following statements is correct ?

aAfter both have travelled 2 km, the distance between them is 4 km.
bThey meet after each has travelled 3 km.
cThey meet for the first time after each has travelled 4 km.
dThey go on without ever meeting again.

AnswerUPSC’s answer is (b).

Put the start at the origin: Shahid goes east and Rohit goes west. After 1 km, Shahid turns left to go north, and Rohit turns right and also goes north. After 2 km they are at the same height, 2 km apart (at (1, 1) and (−1, 1)). At the next turn Shahid turns left to go west and Rohit turns right to go east, so they walk towards each other and meet at (0, 1) after 3 km each.

Why each option is right or wrong
  • (a) Wrong: after 2 km each they are 2 km apart, not 4 km.
  • (b) Right: they meet at the point 1 km north of the start after 3 km each.
  • (c) Wrong: they meet earlier, after 3 km.
  • (d) Wrong: they meet after 3 km.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.