Mensa IQ Test Mensa IQ Logical Deduction Problems

Question 1

All roses are flowers. Some flowers fade quickly. What can be deduced?

Accepted Answer

Some roses may fade quickly

Answer

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?

Accepted Answer

It is not raining

Answer

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?

Accepted Answer

Alice is taller than Charlie

Answer

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?

Accepted Answer

No salmon can fly

Answer

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?

Accepted Answer

A implies C

Answer

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.

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Mensa IQ Test Mensa IQ Logical Deduction Problems