Question

You are on an island inhabited by 3 types of people. Those who only tell the truth (knights), those who only tell lies (knaves) and those who either tell the truth or lie (spies). You come across 3 people. You know that one is a knight, one is a knave and one is a spy.

A says B is a spy
B says C is a spy
C says B is a spy
What type is each person

Answer 1

Step-by-step explanation:

A says B is a spy.

If A is a knight, then B must not be a spy, which means B is a knave or a knight. But if A is a knave, then B could be a spy, but A would be lying. Therefore, A cannot be a knave, so A must be a knight.

B says C is a spy.

If B is a knight, then C must be a spy, which means B would be lying. If B is a knave, then C could be a spy, but B would be telling the truth, which is impossible. Therefore, B cannot be a knave, so B must be a spy.

C says B is a spy.

If C is a knight, then B must not be a spy, which means C would be lying. If C is a knave, then B could be a spy, but C would be telling the truth, which is impossible. Therefore, C cannot be a knave, so C must be a knight.

So, A is a knight, B is a spy, and C is a knight.