UPSC Prelims 2016 · CSAT
Question 78: Basic Numeracy
In a race, a competitor has to collect 6 apples which are kept in a straight line on a track and a bucket is placed at the beginning of the track which is a starting point. The condition is that the competitor can pick only one apple at a time, run back with it and drop it in the bucket. If he has to drop all the apples in the bucket, how much total distance he has to run if the bucket is 5 meters from the first apple and all other apples are placed 3 meters apart ?
AnswerUPSC’s answer is (d).
The apples lie at 5, 8, 11, 14, 17 and 20 m from the bucket (the first at 5 m, then 3 m apart). Each apple needs a round trip of twice its distance. Total = 2 x (5 + 8 + 11 + 14 + 17 + 20) = 2 x 75 = 150 m. Shortcut: the distances form an arithmetic progression, so the sum is 6 terms x average 12.5 = 75.
Why each option is right or wrong
- (a) 40 m is far too short for six round trips.
- (b) 50 m is too short.
- (c) 75 m is the one-way sum only.
- (d) Right: 150 m for six round trips.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2016, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.