UPSC Prelims 2021 · CSAT
Question 18: Logical Reasoning and Mental Ability
A bank employee drives 10 km towards South from her house and turns to her left and drives another 20 km. She again turns left and drives 40 km, then she turns to her right and drives for another 5 km. She again turns to her right and drives another 30 km to reach her bank where she works. What is the shortest distance between her bank and her house ?
AnswerUPSC’s answer is (b).
Use coordinates from the house, as (east, north). South 10 km: (0, −10). A left turn when facing south points east, so 20 km east: (20, −10). Left from east is north: 40 km north: (20, 30). Right from north is east: 5 km east: (25, 30). Right from east is south: 30 km south: (25, 0). The bank is 25 km due east of the house. Remember: a left turn from south faces east, and drawing the path on coordinates avoids slips.
Why each option is right or wrong
- (a) 20 km is the east distance after the second leg; she later goes 5 km further east.
- (b) Right: she ends at (25, 0), 25 km due east of the house.
- (c) 30 km is her last leg south, not the bank's distance from the house.
- (d) 35 km would need extra eastward travel that the route does not have.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.