UPSC Prelims 2000 · General Studies
Question 148: Logical Reasoning and Mental Ability
A person starts from a point A and travels 3 km eastwards to B and then turns left and travels thrice that distance to reach C. He again turns left and travels five times the distance he covered between A and B and reaches his destination D. The shortest distance between the starting point and destination is
AnswerThe answer is (c).
Take A as the origin. A to B is 3 km east. Turning left means going north, so B to C is 3 x 3 = 9 km north. Turning left again means going west, so C to D is 5 x 3 = 15 km west. D is then 15 - 3 = 12 km west and 9 km north of A. The distance is the square root of 12 squared plus 9 squared, which is 15 km.
Why each option is right or wrong
- (a) 18 km adds 3 and 15 instead of taking the net 12 km west.
- (b) 16 km does not fit the 9 and 12 km right-angled triangle, whose hypotenuse is 15.
- (c) Right: the straight-line distance is 15 km.
- (d) 12 km is only the east-west shift and leaves out the 9 km north.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.