2020 CSAT, all questions

UPSC Prelims 2020 · CSAT

Question 9: Basic Numeracy

Let p, q, r and s be natural numbers such that p - 2016 = q + 2017 = r - 2018 = s + 2019

Which one of the following is the largest natural number?

ap
bq
cr
ds

AnswerUPSC’s answer is (c).

Set each expression equal to a common value k. Then p = k + 2016, q = k - 2017, r = k + 2018 and s = k - 2019. The largest is the one with the biggest added amount: r exceeds p by 2, while q and s are both below k. Keep the common value k and compare only the offsets.

Why each option is right or wrong
  • (a) p = k + 2016 is 2 less than r.
  • (b) q = k - 2017 is below k, so far smaller than r.
  • (c) Right: r = k + 2018 has the largest offset.
  • (d) s = k - 2019 is the smallest of the four.

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

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Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.