Paper 1 · Logical Reasoning
Which of the following are correct (valid) ways of reasoning?
- There can be no second husband without there having been a second marriage
- Anil is a friend of Bob; Bob is a friend of Raj; hence Anil is a friend of Raj
- A is equal to B; B is equal to C; hence A is equal to C
- If everyone is a liar, then we cannot prove it
A3 and 4 ✓ Correct
B1 and 3
C2, 3 and 4
D1, 2, 3 and 4
Correct answer: (A) 3 and 4 — Statements 3 and 4 are valid reasoning, so that is the answer.
Explanation
★Statements 3 and 4 are valid reasoning, so that is the answer.
★Equality is transitive, so A equals B and B equals C validly gives A equals C.
★The liar statement is a sound observation about self-reference.
★Friendship is not transitive, so statement 2 is an invalid inference.
★Statement 1 rests on a confused relational claim and is not valid reasoning.
★So the answer is 3 and 4.
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