Mensa IQ Test Mensa IQ Logical Deduction Problems 1 — Questions and Answers
Question 1: All roses are flowers. Some flowers fade quickly. What can be deduced?
- Some roses may fade quickly (Correct answer)
- All roses fade quickly
- No roses fade quickly
- All flowers are roses
Correct answer: Some roses may fade quickly
Since all roses are flowers, and some flowers fade quickly, it's possible that some of those flowers that fade quickly are roses. However, we cannot be certain — we can only say some roses MAY fade quickly.
Question 2: If it rains, the ground gets wet. The ground is not wet. What can you conclude?
- It is not raining (Correct answer)
- It is raining
- The ground is wet
- Nothing can be concluded
Correct answer: It is not raining
This is modus tollens: If P then Q. Not Q. Therefore not P. Since rain always causes wet ground, and the ground isn't wet, it cannot be raining. This is one of the fundamental rules of logical deduction.
Question 3: Alice is taller than Bob. Bob is taller than Charlie. What is true?
- Alice is taller than Charlie (Correct answer)
- Charlie is taller than Alice
- Bob is the tallest
- Alice and Charlie are the same height
Correct answer: Alice is taller than Charlie
Height comparisons are transitive: if A > B and B > C, then A > C. Since Alice is taller than Bob, and Bob is taller than Charlie, Alice must be taller than Charlie.
Question 4: No fish can fly. All salmon are fish. What can be deduced about salmon?
- No salmon can fly (Correct answer)
- Some salmon can fly
- All salmon can fly
- Salmon might fly
Correct answer: No salmon can fly
This is a classic syllogism. Since all salmon are fish, and no fish can fly, it follows that no salmon can fly. The property of 'cannot fly' transfers from the larger category (fish) to the subset (salmon).
Question 5: If A implies B, and B implies C, what can we conclude?
- A implies C (Correct answer)
- C implies A
- B implies A
- A and C are unrelated
Correct answer: A implies C
This is the transitivity of implication (hypothetical syllogism). If A→B and B→C, then A→C. If A is true, B must be true, and if B is true, C must be true. Therefore if A is true, C must be true.
Question 6: In a room of 5 people, everyone shakes hands with everyone else exactly once. How many handshakes occur?
- 10 (Correct answer)
- 20
- 15
- 25
Correct answer: 10
Each of the 5 people shakes hands with 4 others, giving 5×4=20 hand-involvements, but each handshake involves 2 people, so divide by 2: 20/2 = 10. The formula is C(5,2) = 5!/(2!×3!) = 10.
Mensa IQ Test Mensa IQ Logical Deduction Problems 1
All roses are flowers.
Some flowers fade quickly.
What can be deduced?