She asks one of them, is he going to tell me this door leads to the castle.
If answered by the liar, if the door is deadly, then the other guard will say no, but since he lies, he would answer yes.
And if the door leads to the castle, then the real answer is yes, but since he lies, he would say no.
If answered by the truth teller, if the door is deadly, the liar will lie, so he would answer yes. If the door leads to the castle, the liar will lie and the answer is no.
So if the answer is yes then the door being asked is deadly, otherwise the door leads to the castle.
Latest Answers