Knight, Knave, Commoner #1


I got this problem from Rustan Leino, who got it from Carroll Morgan.

I solved it and wrote up my solution.


A king has a daughter and wants to choose the man she will marry. There are three suitors from whom to choose, a Knight, a Knave, and a Commoner. The king wants to avoid choosing the Commoner as the bridegroom, but he does not know which man is which. All the king knows is that the Knight always speaks the truth, the Knave always lies, and the Commoner can do either. The king will ask each man one yes/no question, and will then choose who gets to marry the princess. What questions should the king ask and how should he choose the bridegroom?

Solution     Reveal