There is a land where every inhabitant is either of Type X or Type Y. One type always tells the truth, and one type always lies. You meet two inhabitants, A and B.

A:B is of Type X.
B:At least one of us is of Type Y.

Which type tells the truth, which type lies, and what are A and B?

A & B cannot both be liars.  If A is a liar, then B is type Y making Y's statement true.  Conversely, A & B cannot both be telling the truth.  If by A's statement B is Type X, then A must also be type X, making B's statement a lie.  So one of the statements is false and the other is true.  I.e. one is a liar and the other is not.

B's statement must be true since one of the two has to be type Y.  Thus:

A = Type X - Liar
B = Type Y - Truthful

Posted by hoodat on 2020-01-14 18:18:55