2017 CSAT, all questions

UPSC Prelims 2017 · CSAT

Question 37: Basic Numeracy

There is a milk sample with 50% water in it. If 1/3rd of this milk is added to equal amount of pure milk, then water in the new mixture will fall down to

a25%
b30%
c35%
d40%

AnswerUPSC’s answer is (a).

Take 1 litre of the sample, with 0.5 litre of water. One third of it is 1/3 litre, holding 1/6 litre of water. Adding an equal amount, 1/3 litre of pure milk, gives 2/3 litre of mixture with 1/6 litre of water: (1/6) / (2/3) = 1/4 = 25%. Quicker: the water is now spread over twice the volume, so its share halves from 50% to 25%.

Why each option is right or wrong
  • (a) Correct: the water share halves because the volume doubles.
  • (b) 30% does not match the working.
  • (c) 35% does not match the working.
  • (d) 40% is too high: the water share exactly halves.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedPrevious questionNext question

Source: UPSC, Civil Services (Preliminary) Examination 2017, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.