A king decided to let a prisoner try to escape the prison with his life. The king placed 2 marbles in a jar that was glued to a table. One of the marbles was supposed to be black, and one was supposed to be blue. If the prisoner could pick the blue marble, he would escape the prison with his life. If he picked the black marble, he would be executed. However, the king was very mean, and he wickedly placed 2 black marbles in the jars and no blue marbles. The prisoner witnessed the king only putting 2 black marbles in the jars. If the jar was not see-through and the jar was glued to the table and that the prisoner was mute so he could not say anything, how did he escape with his life?
The prisoner grabbed one of the marbles from the jar and concealed it in his hand. He then swallowed it, and picked up the other marble and showed everyone. The marble was black, and since the other marble was swallowed, it was assumed to be the blue one. So the mean king had to set him free.
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.
You have a sock drawer.
It has 4 black socks, 8 brown socks, 2 white socks and 8 tan socks.
You need to pull out a matching pair of socks in the dark.
There is no light and you couldn't see the socks.
How many socks you should pull out in the dark to get one matching pair of socks?
Five. You have only four different colors of socks. If you pick 5, you can surely get one pair of matching socks.
A guard is stationed at the entrance to a bridge. He is tasked to shoot anyone who tries to cross to the other side of the bridge, and to turn away anyone who comes in from the opposite side of the bridge. You are on his side of the bridge and want to escape to the other side.
Because the bridge is old and rickety, anyone who tries to cross it does so at a constant speed, and it always takes exactly 10 minutes to cross.
The guard comes out of his post every 6 minutes and looks down the bridge for any people trying to leave, and at all other times he sits in his post and snoozes. You know you can sneak past him when he's sleeping, but the problem is that you won't be able to make it all the way to the other side of the bridge before he sees you (since he comes out every 6 minutes, but it takes 10 minutes to cross).
One day a brilliant idea comes to you, and soon you've successfully crossed to the other side of the bridge without being shot. How did you do it?
Right after the guard goes back to his post after checking the bridge, you sneak by and make your way down the bridge. After a little bit less than 6 minutes, you turn around and start walking back toward the guard. He will come out and see you, and assume that you are a visitor coming from the other side of the bridge, since you're only about 4 minutes from the end of the other side of the bridge. He will go back into his post since he doesn't plan to turn you away until you reach him, and then you turn back around and make your way the rest of the way to the other side of the bridge.
You walk into a creepy house by yourself. There is no electricity, plumbing or ventilation. Inside you notice 3 doors with numbers on them. Once you open the doors you will die a particular way.
Door #1 You’ll be eaten by a lion who is hungry.
Door #2 You’ll be stabbed to death.
Door #3 There is an electric chair waiting for you.
Which door do you pick?
Door #3, Since There Is No Electricity To Harm You.
At a local bar, three friends, Mr. Green, Mr. Red and Mr. Blue, were having a drink. One man was wearing a red suit; one a green suit; and the other a blue suit.
"Have you noticed," said the man in the blue suit, "that although our suits have colors corresponding to our names, not one of us is wearing a suit that matches our own names?"
Mr. Red looked at the other two and said, "You're absolutely correct."
What color suit is each man wearing?
Since none of the men are wearing the color of suit that corresponds to their names, and Mr. Red was replying to the man in the blue suit, it had to be Mr. Green to whom he replied. We then know that Mr. Green is wearing a blue suit. Therefore, Mr. Red is wearing a green suit and Mr. Blue is wearing a red suit.