THE PRISONERS'S BOXES

You are the janitor at a prison with 100 prisoners locked in separate, soundproof and windowless cells.

You watch one day as the warden brings the prisoners out to a central room where there are 100 boxes laid out, labeled 1 through 100. He hands each prisoner a slip of paper and a pen, and asks everyone to write their name on their slip and hand it back to him. All the prisoner's have different names.

The warden then makes a proposition to the prisoners. He will put them back in their cells and will put each of the 100 slips of paper into a different box. The prisoners will then be brought out one by one in a random order. When a prisoner comes out, he will get to open 50 boxes. He doesn't need to pre-select which boxes he'll open; he can choose as he goes along. He is also not allowed to rearrange the boxes or the names as he does this.

If any of the 50 boxes he opens contains the slip with that prisoner's name on it, then that prisoner "passes" the test. He will be sent back to his cell, all of the boxes will be closed, and the next prisoner will be brought out. However, if any prisoner opens 50 boxes and none of them contain his name, then all 100 prisoners will be executed. Note that prisoners have no way of passing information on to any of the prisoners who go after them.

If all of the prisoners are able to "pass" the test, then they will all be set free, and you'll receive a big promotion.

Luckily for the prisoners, the warden is going to let you help them in the following way. After he's put all of the names in the boxes, he will bring you into the room, let you look at all the names in all the boxes, and then, if you choose to, switch two names with each other. For example, you could switch the names in boxes 35 and 77. You are only allowed to make one switch.

After you help with this task, you will be sent out of the prison and will not be able to communicate with the prisoners.

Before this strange game begins, you get to meet with the prisoners to discuss a strategy. 

This strategy must have two parts:

1. How do you decide which names to switch, if any at all?
2. How does each prisoner decide which 50 boxes he will open?

What plan do you come up with to ensure that the prisoners will all go free?

[[HINT]]>>

     This is a tough riddle. Here are a few hints:

• If you assign each prisoner a different number between 1 and 100, you can correlate each prisoner with one of the 100 boxes in a manner unrelated to the slips of paper. This could help with the prisoners' process for deciding which boxes to open.
• You need to ensure that certain combinations of names/boxes do or do not arise as the warden puts the slips in the boxes in order to make sure that the prisoners' box-choosing strategy works. You can do this with your switch (if you choose to make one).]]

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PRISONERS AND A LIGHT-BULB

There is a prison with 100 prisoners, each in separate cells, which are sealed off, soundproof and windowless. There is a lobby in the prison with a light-bulb in it. Each day, the warden will pick one of the prisoners at random (even if they have been picked before) and take them out to the lobby. The prisoner will have the choice to flip the light-bulb switch if they want. The light-bulb starts in the "off" position.

When a prisoner is brought out to the lobby, he also has the option of saying "Every other prisoner has been brought out to the lobby." If a prisoner chooses to say this and it is true, all the prisoners will go free. However, if a prisoner chooses to say this and it's wrong, all the prisoners will be executed. So a prisoner should only say this if he knows it is true for sure.

Before the first day of this process begins, all the prisoners are allowed to get together to discuss a strategy to eventually save themselves.

What strategy could they use to ensure their eventual salvation?

(HINT: Try appointing a "lead" prisoner who has a different role than the rest of the prisoners.)

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ANY FIVE CARDS

You meet a magician and his assistant, who decide to show you a trick.

The assistant leaves the room, and the magician hands you an ordinary deck of 52 cards. He has you choose any 5 cards from the deck and give them to him.

He looks over the 5 cards you chose, takes one of them, and hands it back to you.

"That going to be your card," he says. He asks you to put it in your pocket out of sight.

He then takes the four remaining cards and arranges them in a stack in a special order. All four cards in the stack are face-down.

He hands you the stack of four cards and asks you to place them on the table however you like (as long as you don't change the order). He then calls the assistant back in. The assistant picks up the four cards, looks them over, and promptly tells you what your card is.

Note that the magician did not do anything extra to communicate information to the assistant. The only information the assistant has in figuring out your card is the order of the four cards on the table.

How was the assistant able to figure out your card?

(HINT: Because you picked five cards, it's guaranteed that at least two of those cards have the same suit. What if the magician decided to make one of these cards "your" card?) 

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RANDOM AIRPLAIN SEATS

People are waiting in line to board a 100-seat airplane. Ashish is the first person in the line. He gets on the plane but suddenly can't remember what his seat number is, so he picks a seat at random. After that, each person who gets on the plane sits in their assigned seat if it's available, otherwise they will choose an open seat at random to sit in.

The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?

                                         HINT: 

You don't need to use complex math to solve this riddle.

Consider these two questions

What happens if somebody sits in your seat?

What happens if somebody sits in Ashish's assigned seat?

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MASTERS OF LOGIC PUZZLES

MASTERS OF LOGIC PUZZLES - DOTS

Masters of Logic wanted to find out who was the wisest among them.  

So they turned to their Grand Master, asking to resolve their dispute.

"Easy," the old sage said. "I will blindfold you and paint either red or blue dot on each man's forehead. When I take your blindfolds off, if you see at least one red dot, raise your hand. The one, who guesses the color of the dot on his forehead first, wins."

And so it was said, and so it was done. The Grand Master blindfolded the three contestants and painted red dots on every one. When he took their blindfolds off, all three men raised their hands as the rules required, and sat in silence pondering. Finally, one of them said: "I have a red dot on my forehead."

How did he guess?

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MASTERS OF LOGIC PUZZLES – HATS

After losing the "Spot on the Forehead" contest, the two defeated Puzzle Masters complained that the winner had made a slight pause before raising his hand, thus derailing their deductive reasoning train of thought. And so the Grand Master vowed to set up a truly fair test to reveal the best logician among them.

He showed the three men 5 hats - two white and three black.

Then he turned off the lights in the room and put a hat on each Puzzle Master's head.

After that the old sage hid the remaining two hats, but before he could turn the lights on, one of the Masters, as chance would have it, the winner of the previous contest, announced the color of his hat.

And he was right once again. 

What color was his hat? What could have been his reasoning?

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MASTERS OF LOGIC PUZZLES – STAMPS

The Grand Master takes a set of 8 stamps, 4 red and 4 green, known to the logicians, and loosely affixes two to the forehead of each logician. so that each logician can see all the other stamps except those 2 in the Grand Master's pocket and the two on her own forehead.

He asks them in turn if they know the colors of their own stamps:

       A: "No"

       B: "No"

       C: "No"

       A: "No"

       B: "Yes"

       

What color stamps does B have?

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COUNT THE NUMBER OF SQUARES - 1

COUNT THE NUMBER OF SQUARES IN THIS GRID PICTURE

It is a tricky question that has appeared often in mathematical quiz or IQ test math book.

The image is formed by a grid of square lines where reader is asked to count the number of squares. See whether you can answer it correctly or not? How many squares are in this picture? 92% of people FAIL this simple test. Don’t forget to share and give 1 chance to your friends.

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LOGIC PUZZLE: A PING PONG BALL IN A HOLE

Your last good ping-pong ball fell down into a narrow metal pipe embedded in concrete one foot deep.

How can you get it out undamaged, if all the tools you have are your tennis paddle, your shoe-laces, and your plastic water bottle, which does not fit into the pipe?

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LOGIC PUZZLE : BULB

BULBS

There are three switches downstairs. Each corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position.

How would you identify which switch corresponds to which light bulb, if you are only allowed one trip upstairs?

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RIVER CROSSING PUZZLE - 3

SHE-GOAT, WOLF AND CABBAGE

A farmer returns from the market, where he bought a she-goat, a cabbage and a wolf (what a crazy market :-). On the way home he must cross a river. His boat is small and won't fit more than one of his purchases. He cannot leave the she-goat alone with the cabbage (because the she-goat would eat it), nor he can leave the she-goat alone with the wolf (because the she-goat would be eaten).

 

How can the farmer get everything on the other side in this river crossing puzzle?

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RIVER CROSSING PUZZLE -2

FAMILY

Parents with two children - a son and a daughter - came to a wide river. There was no bridge there. The only way to get to the other side was to ask a fisherman if he could lend them his boat. However, the boat could carry only one adult or two children.

How does the family get to the other side and return the boat to the fisherman?

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