The following is a brain teaser:
You are being held prisoner. There are two doors in front of you.
The sign on the door on the left reads “There is a lady behind this door and a tiger behind the other.”
The sign on the door on the right says “There is a lady behind one of the doors and a tiger behind the other.”
Your only clue is this: One of the signs is definitely lying, and one is definitely telling the truth.
The prison guard says “One of these doors leads to freedom, the other leads to certain death. I will give you a chance to choose a door. If you choose the door with the tiger in it, you get eaten. If you choose the door with the lady in it, you are set free.”
It’s possible to determine (without guessing) which door is the correct door, and which one holds the tiger. Is it the door on the left or the door on the right? How do you know for sure which door is the correct door?