There is one prisoner in a prison. This man is sentenced to death by electrocution. But one day, he got a very big favor. The prison manager took this guy and told him:
"This is your only chance to live. Here is a chamber with 2 doors and 2 guards. One door leads directly to electric chair and the other directly to freedom. One guard speaks ONLY truth and the other tell ONLY lies. You do not know which door leads where. In each door stands a guard. You do not know who is who, who tells the truth and who tells lies. You have ONE AND ONLY ONE question to make to ONE ONLY guard. From his answer you must understand which door leads to freedom and pass it. Speak the question"
What is the question?
Remember that he does not know which guard is in front of which door and he only have one question to make to one only guard.
It is not very easy...
