Which of the following statements are logically equivalent? Choose the most appropriate answer from the options given below.

1.Some non-birds are mammals

2.Some birds are not mammals

3.Some non-mammals are non-birds

4.Some non-mammals are not non-birds

A1, 2 and 3 only

B1 and 3 only

C3 and 4 only

D2 and 4 only ✓ Correct

Correct answer: (D) 2 and 4 only

Explanation

Statements 2 and 4 are logically equivalent.

Statement 2 is the particular negative O: Some birds are not mammals.

Full contraposition of an O turns 'Some S are not P' into 'Some non-P are not non-S'.

With S as birds and P as mammals, this gives 'Some non-mammals are not non-birds'.

That is exactly statement 4, so the two are equivalent.

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