UPSC Prelims 2022 · CSAT
Question 39: Logical Reasoning and Mental Ability
Three Statements followed by three Conclusions are given below. You have to take the Statements to be true even if they seem to be at variance from the commonly known facts. Read all the Conclusions and then decide which of the given Conclusions logically follows/follow from the Statements, disregarding the commonly known facts :
- Statement–1Some doctors are teachers.
- Statement–2All teachers are engineers.
- Statement–3All engineers are scientists.
- Conclusion–ISome scientists are doctors.
- Conclusion–IIAll engineers are doctors.
- Conclusion–IIISome engineers are doctors.
Which one of the following is correct?
AnswerUPSC’s answer is (c).
Chain the statements: some doctors are teachers; all teachers are engineers; all engineers are scientists. The doctors who are teachers are therefore engineers, and so scientists. So some engineers are doctors (III) and some scientists are doctors (I) follow. 'All engineers are doctors' (II) does not: only the engineers who are teachers are linked to doctors. A particular premise gives only particular conclusions, and universal conclusions need universal premises.
- I. Doctors who are teachers are engineers and so scientists.
- II. Only engineers who are teachers are linked to doctors.
- III. Doctors who are teachers are engineers.
Why each option is right or wrong
- (a) Incomplete: III also follows.
- (b) Wrong: II does not follow.
- (c) Correct: I and III follow.
- (d) Wrong: II does not follow.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2022, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.