UPSC Prelims 1998 · General Studies
Question 135: Basic Numeracy
If 15 pumps of equal capacity can fill a tank in 7 days, then how many extra pumps will be required to fill the tank in 5 days?
AnswerThe answer is (a).
The work is 15 pumps x 7 days = 105 pump-days. To finish in 5 days, the number of pumps needed is 105 / 5 = 21. The extra pumps required are 21 - 15 = 6. Do not stop at 21, which is the total, not the extra.
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.
This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.
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) Right: 21 - 15 = 6 extra pumps.
- (b) 7 extra pumps give 22, which is more than needed.
- (c) 14 extra gives 29 pumps, which is more than needed.
- (d) 21 is the total number of pumps, not the extra.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1998, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.