On the fabled Island of Knights and Knaves, we meet three people, A, B, and C,…
2024
On the fabled Island of Knights and Knaves, we meet three people, A, B, and C, one of whom is a knight, one a knave, and one a spy. The knight always tells the truth, the knave always lies, and the spy can either lie or tell the truth.A says: "C is a knave". B says: "A is a knight". C says: "I am the spy". Who is the knight?
- A.
A
- B.
B
- C.
C
- D.
B or C
Attempted by 493 students.
Show answer & explanation
Correct answer: A
Answer: A is the knight.
Assume A is the knight:
A's statement "C is a knave" is true, so C is the knave and therefore always lies.
C's statement "I am the spy" must be false (consistent with being the knave). That leaves B as the spy, and the spy is allowed to tell the truth, so B's statement "A is a knight" can be true.
Assume B is the knight:
B's statement "A is a knight" would be true, which would make A a knight as well. That would give two knights, which is impossible, so B cannot be the knight.
Assume C is the knight:
C's statement "I am the spy" would then be true, which is impossible because the knight cannot also be the spy. Therefore C cannot be the knight.
Conclusion:
A = knight
B = spy
C = knave