You are journeying through a forest when you come across a fork in the road. One path will take you out of the forest, while the other will take you deeper into the woods to a deadly swamp.
At the fork, there are two guards with a peculiar sign in front of them. The sign reads:
“One of us always tells the truth, one of us always lies. You may ask exactly one question to just one of us. Choose wisely.”
The two guards look exactly the same and there is no way for you to tell which guard speaks truth and which lies.
What can you ask either guard to take the right path out of the forest?
(Answer after the break)
The correct question to ask is: “If I asked the other guard for directions, which direction would they point me in?”
If you ask the truthful guard, they would know that the lying guard will tell you the wrong directions, therefore they will tell you the wrong directions.
If you ask the lying guard, they would lie and give the opposite direction to the right direction that the truthful guard would tell you.
Ergo, whatever the guard answers to your question, go the opposite direction to that and you will be on the right path.