You're walking down a path and come to two doors. One of the doors leads to a life of prosperity and happiness, and the other door leads to a life of misery and sorrow. You don't know which door is which.
In front of the door is ONE man. You know that this man either always lies, or always tells the truth, but you don't know which. The man knows which door is which.
You are allowed to ask the man ONE yes-or-no question to figure out which door to go through. To make things more difficult, the man is very self-centered, so you are only allowed to ask him a question about what he thinks or knows; your question cannot involve what any other person or object (real or hypothetical) might say.
What question should you ask to ensure you go through the good door?
You should ask: "If I asked you if the good door is on the left, would you say yes?"
Notice that this is subtly different than asking "Is the good door on the left?", in that you are asking him IF he would say yes to that question, not what his answer to the question would be. Thus you are asking a question about a question, and if it ends up being the liar you are talking to, this will cause him to lie about a lie and thus tell the truth. The four possible cases are:
The man is a truth-teller and the good door is on the left. He will say "yes".
The man is a truth-teller and the good door is on the right. He will say "no".
The man is a liar and the good door is on the left. He will say "yes" because if you asked him "Is the good door on the left?", he would lie and say "no", and so when you ask him if he would say "yes", he will lie and say "yes".
The man is a liar and the good door is on the right. Similar to the previous example, he'll say "no".
So regardless of whether the man is a truth-teller or a liar, this question will get a "yes" if the door on the left is the good door, and a "no" if it's not.
See also best riddles or new riddles.logicmathshort
Can you arrange four 9's and use of atmost 2 math symbols, make the total be 100?
99 / .99logicmysteryscary
A man was shot to death while in his car. There were no powder marks on his clothing which indicated that the gunman was outside the car. However, all the windows were up and the doors locked. After a close inspection was made, the only bullet holes discovered were on the man's body. How was he murdered?
The victim was in a convertible.logic
Allan, Bertrand, and Cecil were caught stealing so the king sent them to the dungeon.
But the king decided to give them a chance.
He mad them stand in a line and put hats on their heads.
He told them that if they answer a riddle, they could go free.
Here is the riddle: "Each of you has a hat on your head. You do not know the color of the hat on your own head. If one of you can guess the color of the hat on your head, I will let you free. But before you answer you must keep standing in this line. You cannot turn around. Here are my only hints: there are only black and white hats. At least one hat is black. At least one hat is white."
Allan couldn't see any hats.
Bertrand could see Allan's hat but not his own.
Cecil could see Bertrand's hat and Allan's hat, but not his own.
After a minute nobody had solved the riddle. But then a short while later, one of them solved the riddle. Who was is and how did he know?
Bertrand knew the answer because Cecil didn't say anything after one minute. If Bertrand and Allan's hats were both the same color, then Cecil would know what color his hat was. But Cecil didn't know. So Bertrand knew that Allan's hat was a different color than his. Since Allan's hat was black, Betrand knew his hat was white. cleanlogicshort
You draw a line. Without touching it, how do you make the line longer?
You draw a shorter line next to it, and it becomes the longer line.logicshortwhat am I
I have keys but no locks. I have a space but no room. You can enter, but can’t go outside. What am I? I have a space but no room. You can enter, but can’t go outside. What am I?
A woman shoots her husband, then holds him under water for five minutes. A little while later, they both go out and enjoy a wonderful dinner together. How can this be?
She shot her husband with a camera and then developed the photo. cleanlogicmathshort
Would you have more money with a million dollars today or a penny today and double your money every day for 31 days?
Second option. Double your money every day for 31 days.logic
A young boy went to a Catholic school. During school he started goofing around, so the teacher called him out and sent him to the Pastor. Since this was a traditional school the boy would be spanked, but the Pastor believed in giving people a chance. He said, "If you can ask me a question about something you learned and I don't know the answer on the spot you will go free." The boy may have been lazy, but he was very witty. He asked, "What is it that you can see and I can see, usually every day, but God cannot see." The Pastor stood there, stumped. He couldn't figure it out because he strongly believed that God sees and knows all, and that there is only one God. The boy smiled and told him.
What was it?
His own equal! We see our equals everyday, but since there is one God, he cannot see someone equal to himself. logic
In a small town in the United States, a teenage boy asked his parents if he could go to a friend's party. His parents agreed, provided that he was back before sunrise. He left the house that evening clean-shaven and when he returned just before the following sunrise his parents were amazed to see that he had a fully grown beard. What happened?
The small town was Barrow in Alaska, the northernmost town in the United States. When the sun sets there in the middle of November, it does not rise again for 65 days. That allowed plenty of time for the boy to grow a beard before the next sunrise. cleanlogicshort
A beggar's brother died, but the man who died had not brother.
How could this be?
The beggar was a women.