Mensa IQ Deductive Reasoning Puzzles Questions and Answers

Question 1

On an island inhabited only by knights (who always tell the truth) and knaves (who always lie), you meet three inhabitants: Alex, Ben, and Carl.
Alex says, 'Ben is a knave.' Ben says, 'Alex and Carl are of the same type.' Carl says, 'I am a knight.' Which of the following is true?

Accepted Answer

Alex is a knave, Ben is a knight, Carl is a knave.

Answer

Alex is a knight, Ben is a knave, Carl is a knight.

Answer

Alex is a knave, Ben is a knave, Carl is a knave.

Answer

Alex is a knight, Ben is a knight, Carl is a knave.

Question 2

Given the following premises, which conclusion logically follows?
1. All squares are rectangles.
2. No rectangles are circles.
3. Some rhombuses are squares.

Accepted Answer

Some rhombuses are not circles.

Answer

All squares are circles.

Answer

No squares are rhombuses.

Answer

Some circles are squares.

Question 3

Five colleagues (Frank, Gina, Henry, Iris, Jack) each work on a different floor (1, 2, 3, 4, 5) of an office building. 
- Gina works on a floor two levels below Henry.
- Frank works on a floor above Iris.
- Jack works on an odd-numbered floor, but not the first floor.
- Henry works on the top floor.
Which of the following statements is true?

Accepted Answer

Frank works on the 4th floor.

Answer

Gina works on the 2nd floor.

Answer

Iris works on the 1st floor.

Answer

Jack works on the 5th floor.

Question 4

In a logic grid puzzle, if you determine that 'The person who owns the cat lives in the Blue house,' which of the following deductions is also immediately true based on the standard rules of these puzzles?

Accepted Answer

The person in the Blue house does not own the dog.

Answer

The person in the Green house might own the cat.

Answer

The person who owns the dog might live in the Blue house.

Answer

Anyone who does not own the cat lives in the Blue house.

Question 5

A detective finds four statements at a crime scene. It is known that exactly one statement is true.
- Statement A: 'Statement C is false.'
- Statement B: 'Statement D is true.'
- Statement C: 'I am not the true statement.'
- Statement D: 'Statement B is a lie.'

Which statement is the true one?

Accepted Answer

Statement C

Answer

Statement A

Answer

Statement B

Answer

Statement D

Question 6

Premise 1: If it is raining, the street is wet. Premise 2: The street is not wet. What is the valid deductive conclusion?

Accepted Answer

It is not raining.

Answer

It is raining.

Answer

The street is wet because it is raining.

Answer

Sometimes when it rains, the street is not wet.

On an island inhabited only by knights (who always tell the truth) and knaves (who always lie), you meet three inhabitants: Alex, Ben, and Carl.Alex says, 'Ben is a knave.' Ben says, 'Alex and Carl are of the same type.' Carl says, 'I am a knight.' Which of the following is true?

On an island inhabited only by knights (who always tell the truth) and knaves (who always lie), you meet three inhabitants: Alex, Ben, and Carl.
Alex says, 'Ben is a knave.' Ben says, 'Alex and Carl are of the same type.' Carl says, 'I am a knight.' Which of the following is true?