2020 CSAT, all questions
UPSC Prelims 2020 · CSAT
Question 29: Data Interpretation
Two Statements S1 and S2 are given below followed by a Question :
- S1n is a prime number.
- S2n leaves a remainder of 1 when divided by 4.
- QuestionIf n is a unique natural number between 10 and 20, then what is n?
Which one of the following is correct in respect of the above Statements and the Question?
aS1 alone is sufficient to answer the Question.
bS2 alone is sufficient to answer the Question.
cS1 and S2 together are sufficient to answer the Question, but neither S1 alone nor S2 alone is sufficient to answer the Question.
dS1 and S2 together are not sufficient to answer the Question.
AnswerUPSC’s answer is (d).
S1 alone: the primes between 10 and 20 are 11, 13, 17 and 19, so it does not fix n. S2 alone: numbers in that range that leave remainder 1 on division by 4 are 13 and 17, so two possibilities. Together: both 13 and 17 are prime and leave remainder 1, so two candidates remain and n cannot be pinned down.
Why each option is right or wrong
- (a) S1 alone leaves four primes.
- (b) S2 alone leaves 13 and 17.
- (c) Together they still leave 13 and 17, so they are not sufficient.
- (d) Right: even together, n could be 13 or 17.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.