2020 CSAT, all questions

UPSC Prelims 2020 · CSAT

Question 77: Basic Numeracy

A digit n > 3 is divisible by 3 but not divisible by 6. Which one of the following is divisible by 4?

a2n
b3n
c2n + 4
d3n + 1

AnswerUPSC’s answer is (d).

A digit above 3 that is divisible by 3 is 6 or 9. Not divisible by 6 rules out 6, so n = 9. Test each option: 2n = 18, 3n = 27, 2n + 4 = 22, 3n + 1 = 28. Only 28 is divisible by 4 (28 = 4 × 7).

Why each option is right or wrong
  • (a) 18 is not divisible by 4.
  • (b) 27 is odd.
  • (c) 22 leaves remainder 2 on division by 4.
  • (d) Right: 28 = 4 × 7.

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.