UPSC Prelims 2013 · CSAT
Question 65: Basic Numeracy
The tank-full petrol in Arun’s motor-cycle lasts for 10 days. If he starts using 25% more everyday, how many days will the tank-full petrol last ?
AnswerUPSC’s answer is (d).
Treat the full tank as 10 units, used at 1 unit a day. If daily use rises by 25 per cent to 1.25 units, the tank lasts 10 / 1.25 = 8 days. In general, when use goes up by a factor, the time goes down by the same factor: 10 days divided by 1.25 gives 8 days.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong. 5 days would mean double the daily use.
- (b) Wrong. 6 days would mean about 1.67 times the use.
- (c) Wrong. 7 days would mean about 1.43 times the use.
- (d) Right. 10 / 1.25 = 8 days.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.