All Puzzles

  • Army General, accused of high disloyalty, is sentenced to death by the court-martial. He is allowed to make a final statement, after which he will be shot if the statement is false or will be hung if the statement is true. General makes his final statement and is released.

    What could he have said?

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  • Four white pieces (the mice) are placed on one side of a chessboard, and one black piece (the cat) is placed at the opposite side. The game is played by the following rules:

    black wins if it reaches the opposite side;
    white wins if it blocks black in such a way that black cannot make any move anymore;
    only diagonal moves (of length 1) on empty squares are allowed;
    white only moves forward;
    black can move backward and forward;
    black may make the first move, then white makes a move, and so on.

    Is this game computable (i.e. is it possible to decide beforehand who wins the game, no matter how hard his opponent tries to avoid this)?

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  • A stopped clock gives the exact time twice a day, while a normally running (but out of sync) clock will not be right more than once over a period of months. A clever grandfather [as in grandfather clock] adjusted his clock to give the correct time at least twice a day, while running at the normal rate. Assuming he was not able to set it perfectly, how did he do it?

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    • 119 views
    • 1 answers
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  • Jacob and John are competing for the same girl. After years of battling, both decide to settle it by tossing a coin.

    John produces a coin, but Jacob doesn’t happen to have one on him. Jacob is sure that the coin John has produced is loaded, i.e. it will come up with heads more than 50% of the time on average.

    How do Jacob arrange a fair contest, based purely on chance and not skill, by flipping this coin?

    Variation: (COIN BIASING) Jacob and John are competing for the same girl, and decide to settle it with a coin toss. John has known the girl longer than Jacob have, so Jacob agree that it is fair for him to have a chance of winning equal to P, where P > 0.5. However, Jacob only have a fair coin. How can you conduct this contest such that the biased probability is manifested? What is the average number of coin flips needed to determine a winner?

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  • A prisoner fate will be determined by a game. there are two jars, one with 100 white marbles, and one with 100 black marbles. at this point, prisoner is allowed to redistribute the marbles however he wish e.g. swap a black marble with a white marble, etc. the only requirement is that after prisoner is done with the redistribution, every marble must be in one of the two jars. Afterwards, both jars will be shaken up, and prisoner will be blindfolded and presented with one of the jars at random. then he pick one marble out of the jar given to him. if the marble prisoner pull out is white, prisoner live; if black, prisoner die. how should prisoner redistribute the marbles to maximise the probability that he live; what is this maximum probability (roughly)?

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    • 196 views
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  • You want to send a valuable object to a friend.

    You have a box which is more than large enough to contain the object.

    You each have several locks with keys, but not keys to each other’s locks.

    The box has a locking ring which is large enough to have many locks attached.

    You cannot send a key in an unlocked box, since it might be copied.

    How do you do it?

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    • 243 views
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  • A man every day goes to office 2 hours late and comes after 2 hours. he goes to office by lift up to 9th floor and more 3 floors goes by walking but while returning he comes by lift from 12th floor, why?

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    • 392 views
    • 2 answers
    • -1 votes



  • John was in his car when he finds that one of the wheels was missing. John cannot get out of the car as there was a brutal killer nearby him.
    Still, John easily escapes. How?

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    • 342 views
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  • Last night, I was looking at a road sign and could see that Leeds was 13 miles away, Stoke was 13 miles away and Leek was 10 miles away.

    Unfortunately it was too dark to see how far it was to Manchester. Can you help me?

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  • Yesterday John’s mother asked him to buy some stamps. Stamps, in the land of Puzzlefry, are available in 3p, 9p, 11p, 17p and 21p denominations.

    For three types of stamp John was asked to buy eight of each. For the other two types of stamp, he was asked to buy nine of each.

    Unfortunately he forgot which he was supposed to buy eight of and which to buy nine of.

    Luckily his mother had given him the exact money required to buy the stamps, £5.00 and the shopkeeper was able to give him the correct stamps.

    Which stamps did he buy?

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    • 237 views
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