UPSC Prelims 2001 · General Studies
Question 142: Basic Numeracy
Water is filled in a container in such a manner that its volume doubles after every five minutes. If it takes 30 minutes for the container to be full, in how much time will it be one-fourth full?
AnswerThe answer is (c).
The volume doubles every five minutes and the container is full at 30 minutes. So 5 minutes earlier (25 minutes) it was half full, and 10 minutes earlier (20 minutes) it was one-fourth full. Remember to work backwards from the full stage when something doubles at fixed intervals.
Why each option is right or wrong
- (a) 7.5 minutes is far too early, as the volume would be tiny.
- (b) At 10 minutes the container would be only 1/16 full.
- (c) Right: 20 minutes.
- (d) At 25 minutes the container is half full.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.