GCAT Syllogistic Reasoning 5 — Questions and Answers
Question 1: No mammals lay eggs. Platypuses lay eggs. What must follow?
- Platypuses are mammals.
- Platypuses are not mammals. (Correct answer)
- Some mammals lay eggs.
- Platypuses might be mammals.
Correct answer: Platypuses are not mammals.
By contrapositive, if something lays eggs it cannot be a mammal.
Question 2: All optimists are happy. All happy people sleep well. Some night-shift workers do not sleep well. Which follows?
- Some night-shift workers are not optimists. (Correct answer)
- All night-shift workers are optimists.
- Some optimists work night shifts.
- No night-shift workers are happy.
Correct answer: Some night-shift workers are not optimists.
Optimists → happy → sleep well; those who don't sleep well are not happy, hence not optimists — applying to the night-shift workers who don't sleep well.
Question 3: All P are Q. No R are Q. Some S are R. Which is valid?
- Some S are P.
- Some S are not Q. (Correct answer)
- All S are P.
- Some S are Q.
Correct answer: Some S are not Q.
The S that are R are not Q (since no R are Q), so at least some S are not Q.
Question 4: Some teachers are strict. All strict people demand discipline. Which must be true?
- All teachers demand discipline.
- Some teachers demand discipline. (Correct answer)
- No teachers demand discipline.
- All who demand discipline are teachers.
Correct answer: Some teachers demand discipline.
Strict teachers must demand discipline, so at least some teachers demand discipline.
Question 5: All carnivores eat meat. This creature does not eat meat. Which conclusion is valid?
- This creature is a carnivore.
- This creature is not a carnivore. (Correct answer)
- This creature might be a carnivore.
- This creature is an herbivore.
Correct answer: This creature is not a carnivore.
Contrapositive of 'all carnivores eat meat' is 'not eating meat means not a carnivore.'
Question 6: No politicians are honest. Some honest people are brave. Which is valid?
- Some politicians are brave.
- No politicians are brave.
- Some brave people are not politicians. (Correct answer)
- All brave people are politicians.
Correct answer: Some brave people are not politicians.
Honest people are brave (some of them), and honest people are not politicians, so those brave honest people are not politicians.
Question 7: All valid arguments have true conclusions. This argument has a false conclusion. What follows?
- This argument is valid.
- This argument might be valid.
- This argument is not valid. (Correct answer)
- All arguments with false conclusions are valid.
Correct answer: This argument is not valid.
By contrapositive, a false conclusion means the argument is not valid.
GCAT Syllogistic Reasoning 5
No mammals lay eggs.
Platypuses lay eggs.
What must follow?