Logical Deduction Problems Flashcards

Six people — F, G, H, I, J, K — are seated in two rows of three facing each other. F faces G. H is to the right of F. I is to the left of G. Who sits opposite H?

Answer: I

F faces G; H is to F's right in one row; I is to G's left in the opposite row, placing I directly opposite H.

No cold-blooded animals are mammals. Dolphins are mammals. Which conclusion is logically valid?

Answer: Dolphins are not cold-blooded

Since dolphins are mammals and no mammals are cold-blooded, dolphins cannot be cold-blooded.

Whenever there is fog, flights are delayed. Flights are delayed today. What can you conclude?

Answer: There may or may not be fog today

Fog causes delays, but delays can have other causes, so fog is not guaranteed from delays alone.

All fast runners are good athletes. Mark is not a good athlete. What must be true about Mark?

Answer: Mark is not a fast runner

By contrapositive, if Mark is not a good athlete, he cannot be a fast runner.

Three friends each prefer a different color: red, blue, or green. Anna does not like red. Ben does not like blue. If Carlos likes green, what does Anna like?

Answer: Blue

Carlos takes green, leaving red and blue; Anna cannot have red, so Anna must like blue.

Statement: 'All honest people keep their promises.' Sandra kept her promise. What can be concluded?

Answer: Sandra may or may not be honest

Keeping a promise is a result of being honest, but others who are not honest could also keep promises.

If A then B. If B then C. If C then D. A is true. Which set of conclusions must all be true?

Answer: B, C, and D

Starting from A, each conditional fires in sequence: A→B→C→D, so B, C, and D are all true.