UPSC Prelims 2017 · CSAT
Question 13: Logical Reasoning and Mental Ability
Four tests—Physics, Chemistry, Mathematics and Biology are to be conducted on four consecutive days, not necessarily in the same order. The Physics test is held before the test which is conducted after Biology. Chemistry is conducted exactly after two tests are held. Which is the last test held?
AnswerUPSC’s answer is (c).
Four tests on four consecutive days. Chemistry is held after exactly two tests, so it is on day 3. The test right after Biology must come after Physics. Biology on day 1 puts that test on day 2, which would need Physics on day 1, already taken by Biology: impossible. Biology on day 2 puts Chemistry right after it on day 3, with Physics on day 1. So the order is Physics, Biology, Chemistry, Mathematics, and Mathematics is last.
Why each option is right or wrong
- (a) Physics is on day 1.
- (b) Biology is on day 2.
- (c) Correct: the order is Physics, Biology, Chemistry, Mathematics.
- (d) Chemistry is fixed on day 3.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2017, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.