Logically Speaking ...
If you do not know this, I assure you it is not easy. And if you get it right without checking the answer? Then, you are a very clever person!
THE LOGICAL TERROR:
His eyes slowly open and he finds himself stood in what appears to be a dark, wet dungeon with moldy green walls. In front of him stands a table with a scroll lay upon it. He looks deeper into his surroundings.
The dungeon is square in shape. He looks to the left wall and sees a huge, solid wooden door which is steel strapped and studded with iron rivets through huge hinges and an equally huge lock with a key already inserted into it. Looking to his right side, he sees another door which is built in the same manner. There are two men in the room and they each stand in front of one of the two doors; they are wearing long hooded shrouds, the hoods hang so low he cannot see their faces. He turns around to see there is no door behind him; as if he had been transported into the dungeon in his sleep. The hooded men both lift up their arms from their sides and with bent, crooked fingers they point to the scroll that lies on the table. He feels afraid as he lowers his head, picks up the scroll and unrolls it to read its content. He reads what is inscribed upon it:
“I brought you from your sleep and I want to take you to a deep, dark place from which you will not return; but I have a weakness which might benefit you. Read well the words that follow … and think hard.”
“You will see the two doors that leave from this place; the keys are in the locks, you only have to turn them, but once turned you cannot go back; do not be tempted to leave before reading the consequences of your actions. One of these doors leads to certain freedom … whilst the other leads to a certain death; ultimately it will be your free choice from which door you leave this place and so it will be you who decides your own Fate. I said I have a weakness that may benefit you; it is in allowing you a hint. Here it is.”
“The men you see before you; consider them well. One of them is a liar and cannot be trusted, for he tells lie after lie and not one true word of truth has ever passed his lips for he does not know how to speak the truth. Another of them always tells the truth; never in his life has he told a lie and a lie he can never tell. They both know each other’s ways. You may ask one question only and you can ask either of the two men; remember, one question only. You have five minutes to choose which door you will pass through; after that time this dungeon will fill with fumes that will suffocate you and I will take you regardless. Your time starts now.”
The man drops the scroll on the table and paces for some minutes and suddenly realizes he has the question he needs. He hurries over to one of the men in the hooded shroud and asks him the question. At getting his response the man yells out “Thank you for saving my life!” and then hastily runs and unlocks one of the doors *knowing * that the door he now unlocks and runs through leads to certain freedom, where he will awaken safely and still in his bed.
QUESTION OF LOGIC:
What question did the man ask one of the men to *know* that the door he went through would lead to *certain* freedom?
(Spend a bit of time thinking about it. If you feel it hopeless, then scroll down to find the Logical Answer)
5. (Halfway … sure you give up?)
THE QUESTION HE ASKED:
It didn’t matter which of the two men he approached; it made no difference. He went to one of the two men guarding the doors and asked this question: “If I was to ask the *other* man which door would lead to certain freedom, which door would he tell me to go through?”
After he was given the answer, he went through the *opposite* door to what he was told.
So … How did he know to do this and be certain of freedom?
If he asked the question to the man who was a liar who always tells lies, he would guide him to the door to certain death, because he is an outright liar. So, he would walk through the *opposite* door he would tell him to do.
If he asked the question to the man who always told the truth, the man would know that the other guy would tell a lie, so he would be forced to tell him what the liar would say (even though he knows it would be a lie, he would have to say what the liar would say in order to tell the truth) and guide him to the door to certain death. So, yet again, he would walk through the *opposite* door.