UPSC Prelims 1995 · General Studies
Question 149: Logical Reasoning and Mental Ability
Which of the following can be inferred from the statement that “Either John is stupid or John is lazy”? I. John is lazy / therefore, John is not stupid. II. John is not lazy / therefore, John is stupid. III. John is not stupid / therefore, John is lazy. IV. John is stupid / therefore, John is not lazy. Choose the correct answer from the codes given below:
AnswerThe answer is (b).
'Either John is stupid or John is lazy' is read as: at least one of them is true. So if one is false, the other must be true: 'not lazy, therefore stupid' (II) and 'not stupid, therefore lazy' (III) follow. But I and IV assume that both cannot be true together, which the statement does not say. Remember: from an either-or, denying one part gives the other.
- I. John may be both lazy and stupid, so being lazy does not rule out being stupid.
- II. If he is not lazy, the other part must hold: he is stupid.
- III. If he is not stupid, the other part must hold: he is lazy.
- IV. Being stupid does not rule out being lazy as well.
Why each option is right or wrong
- (a) I does not follow, since John may be both lazy and stupid.
- (b) Right: II and III.
- (c) IV does not follow, since John could be both.
- (d) I and IV both assume he cannot be both.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1995, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.