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Fact 1: Humans are mammals. Fact 2: Some humans are engineers. Fact 3: Engineers build houses. If the above statements are facts, which of the following can be logically inferred? I. All mammals build houses. II. Engineers are mammals. III. Some humans are not engineers.

Fact 1: Humans are mammals. Fact 2: Some humans are engineers. Fact 3: Engineers build houses. If the above statements are facts, which of the following can be logically inferred? I. All mammals build houses. II. Engineers are mammals. III. Some humans are not engineers. Correct Answer <p>II only</p>

Let us consider each statement separately.
I. All mammals build houses.
This is clearly false as only some mammals (humans) are engineers.
II. Engineers are mammals.
All engineers are definitely humans, and all humans are mammals, therefore this is true.
III. Some humans are not engineers.
The given information states that ‘some humans are engineers’. Therefore, we cannot determine how many humans are engineers. There is the possibility of all humans being engineers as well, so this is definitely false.
Therefore, only II is true.

Mistake Points

1) If the statements are positive, then the negative conclusions will be false in definite cases and vice versa.

2) "Some" does not say anything certain about "Some not".
3) The conclusion must be 100% true. The conclusions which are 99% true will be considered false.
For Example:

Statement: Some A are B  

Conclusion: some A are not B, It is possible, not definite. We can't say anything about the negative conclusion.

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