UPSC Prelims 2024 · CSAT
Question 56: Logical Reasoning and Mental Ability
A person walks 100 m straight from his house, turns left and walks 100 m, again turns left and walks 300 m, then turns right and walks 100 m to reach his office. In which direction does he walk initially from his house if his office is exactly in the North-East direction?
AnswerUPSC’s answer is (c).
Let the first walk be along direction u and let l be the direction to its left. The path is 100u, then 100 l, then 300 in the direction opposite to u (a second left turn), then a right turn from that direction points along l again, for 100 more. The net displacement is −200u + 200l. For this to point north-east, l must be east and u south, since east minus south is east plus north. So he starts walking south.
Why each option is right or wrong
- (a) Wrong. Starting north-west gives a net displacement due south.
- (b) Wrong. Starting west gives a net displacement towards the south-east.
- (c) Right. Starting south makes the net displacement 200 north and 200 east.
- (d) Wrong. Starting south-west gives a net displacement due east.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2024, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.