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On an island there are three types of inhabitants: knights (they always tell the truth), squires (they always lie) and spies (they can lie or tell the truth). You meet three people: A, B and C.
You know that there is exactly one knight, one squire and one spy among them. A says: 'I'm the spy.' B says, 'That's true.' C says: 'I'm not the spy.' What is each one?
Answer: A is the knave, B is the spy, C is the knight.
Rules reminder:
Analysis of the statements:
Statement of A: "I am the spy"
If A were a knight, his sentence (“I am a spy”) would be impossible. So A cannot be a knight.
If A is a knave, his sentence is a lie, so A is not a spy: this does fit.
Conclusion: A = squire.
B's statement: "That is true" (confirms that A is a spy)
Since A is a knave (not a spy), B is stating something false.
So B cannot be a knight, and he cannot be a squire either (A already is).
Conclusion: B = spy.
Statement of C: "I am not the spy"
By elimination, C is the gentleman, and his sentence (“I am not a spy”) is true.
Final answer:
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