Gold box problem

There are ā€˜nā€™ gold boxes placed in a row, each having different number of gold coins.
2 players play a game, where the motive is to collect the maximum number of gold coins. Each player can see how many coins are present in each box, but can get a box from either end only, on his turn.
Design a strategy such that Player1 wins (Assuming both players play smartly)

Source: Amazon Interview

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Duck and Fox

A duck is swimming at the center of a circle-shaped lake. A fox is waiting at the shore, not able to swim, willing to eat the duck. It may move around the whole lake with a speed four times faster than the duck can swim. Can the duck always reach the shore without being eaten by the fox?

Source: Raphael Reischuk Riddles

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Hats on a Death Row

You are one of 20 prisoners on death row with the execution date set for tomorrow. Your king is a ruthless man who likes to toy with his people’s miseries. He comes to your cell today and tells you:
“I’m gonna give you prisoners a chance to go free tomorrow. You will all stand in a row (queue) before the executioner and we will put a hat on your head, either a red or a black one. Of course you will not be able to see the color of your own hat; you will only be able to see the prisoners in front of you with their hats on; you will not be allowed to look back or communicate together in any way (talking, touching…..).

The prisoner in the back will be able to see the 19 prisoners in front of him. The one in front of him will be able to see 18…

Starting with the last person in the row, the one who can see everybody in front of him, he will be asked a simple question: WHAT IS THE COLOR OF YOUR HAT?

He will be only allowed to answer “BLACK” or “RED”. If he says anything else you will ALL be executed immediately.

If he guesses the right color of the hat on his head he is set free, otherwise he is put to death. And we move on to the one in front of him and ask him the same question and so on…

Well, good luck tomorrow, HA HA HA HA HA HA!”

Now since you all can communicate freely during the night, can you find a way to guarantee the freedom of some prisoners tomorrow? How many?


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2 Goats and 1 Car

You are on a game show and there are three doors. The presenter tells you that behind one of doors there is a car and behind the other two are goats. If you pick the car you win it. After you have picked a door the presenter opens a different door with a goat behind it, he then gives you the chance to change what door you open. What should you do?

Hint: It is not 1/2 as you would first think.

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The Dream Job

You are one of the 125 candidates that have been shortlisted to appear for an interview for a job in the company Amgon that pays five lakhs per month. Mr. Donny, a representative of Amgon is in the interviewing panel and he is responsible to select only one candidate for the job. He gives each candidate the same task in which he gives three dice each to every candidate. No marking of any kind has been done on any of the six faces of the dice. He tells them to write one letter each on all the faces of the three dice so that the top faces of the dice can show first three letters of all the months in the year. Can you complete the task and get the job?


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One Cord

You are given one cord that burns exactly one hour, not necessarily with constant speed.
How should you light the cord in order to determine a time interval of 15 minutes?
(Hint: solve the Two Cord puzzle first.)

Source: Raphael Reischuk

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Two Cords

You are given two cords that both burn exactly one hour, not necessarily with constant speed.
How should you light the cords in order to determine a time interval of exactly 15 minutes?

Source: Raphael Reischuk

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Chess Board Puzzle

You’ve got an 8Ɨ8 chess Board and a bunch of dominoes that each fit nicely on two squares of the chess Board.  You can easily tile the entire checkerboard with these dominoes. Now say that you remove two squares, one at one corner and the other at the opposite corner. You’re left with 62 squares.
Can you tile this with the dominoes?
If so, show how. If not, prove why not.


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Chess Board Puzzle

A semi-infinite chess board (vary from zero to infinity in both dimensions) with counters in the three bottom left squares, as shown in the below figure.

How to move: If the squares above and to the right are free, a counter can be removed and replaced by two counters, one in the square above and one in the square to the right – check below

Prove that it is not possible to leave the three bottom left squares empty.

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Black and White Squares Puzzle

Consider an n x n chessboard, where each square is arbitrarily chosen to be either black or white. Your goal is to make all squares in the chessboard white. At each step, you are allowed to “switch” a square, but each switch will toggle not only the particular square being switched, but also the 4 squares that are adjacent to it: Two vertically up and down and two horizontally up and down the square being switched.
Note : At corners only 4/3 squares are toggled, while at the center all 5 squares are toggled.

How you can make the entire chessboard white.
Found at :

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