Which of the following statements are logically equivalent?

1.Some fishes are not amphibians

2.Some fishes are amphibians

3.Some fishes are non-amphibians

4.Some non-amphibians are not non-fishes

A1 & 2 only

B1, 2 & 3 only

C1, 3 & 4 only ✓ Correct

D3 & 4 only

Correct answer: (C) 1, 3 & 4 only

Explanation

Statements 1, 3 and 4 all carry the same particular negative content.

Statement 1 is Some fishes are not amphibians, an O proposition.

Statement 3 is its obverse, Some fishes are non-amphibians, which is logically equal.

Statement 4 is its contrapositive, Some non-amphibians are not non-fishes, valid for O.

Statement 2 is the affirmative I and is not equivalent.

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