UPSC Prelims 2021 · CSAT
Question 10: Logical Reasoning and Mental Ability
A Statement followed by Conclusion-I and Conclusion-II is given below. You have to take the Statement to be true even if it seems to be at variance from the commonly known facts. Read all Conclusions and then decide which of the given Conclusion(s) logically follows/follow from the Statement, disregarding the commonly known facts.
- StatementSome radios are mobiles. All mobiles are computers. Some computers are watches.
- Conclusion-ICertainly some radios are watches.
- Conclusion-IICertainly some mobiles are watches.
Which one of the following is correct ?
AnswerUPSC’s answer is (d).
Draw the sets. Some radios lie inside mobiles, and all mobiles lie inside computers. Some computers are watches, but those watch-computers could all sit outside the mobiles. So no certain link joins radios or mobiles with watches. Conclusion I (radios are certainly watches) and Conclusion II (mobiles are certainly watches) both fail, since each needs the watches to overlap the mobiles, which is not guaranteed. Remember: a 'some' statement about a big set does not reach a smaller set inside it.
- I. Radios and watches need not overlap; the mobile radios may be computers that are not watches.
- II. Mobiles need not be among the computers that are watches.
Why each option is right or wrong
- (a) Conclusion I needs radios to overlap watches; the watches may lie wholly outside the mobiles, so it is not certain.
- (b) Conclusion II needs mobiles to overlap watches; the watch-computers may all be non-mobile computers.
- (c) Neither conclusion is certain, so they cannot both follow.
- (d) Right: the watches that are computers may lie wholly outside the mobiles, so neither is certain.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.