UPSC Prelims 2005 · General Studies
Question 98: Basic Numeracy
Aryan runs at a speed of 40 metre/minute. Rahul follows him after an interval of 5 minutes and runs at a speed of 50 metre/minute. Rahul’s dog runs at a speed of 60 metre/minute and starts along with Rahul. The dog reaches Aryan and then comes back to Rahul, and continues to do so till Rahul reaches Aryan. What is the total distance covered by the dog?
AnswerThe answer is (d).
Aryan has a head start of 40 × 5 = 200 m. Rahul gains 50 − 40 = 10 m a minute, so he catches Aryan after 200/10 = 20 minutes. The dog runs at 60 m a minute for exactly those 20 minutes, covering 60 × 20 = 1200 m, however many times it turns back.
Why each option is right or wrong
- (a) 600 m would be only 10 minutes of the dog's running.
- (b) 750 m does not match 20 minutes at 60 m a minute.
- (c) 980 m does not match 20 minutes at 60 m a minute.
- (d) Correct: 60 × 20 = 1200 m.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2005, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.