All Puzzles

  • There is an island of monks where everyone has either brown eyes or red eyes. Monks who have red eyes are cursed, and are supposed to commit suicide at midnight. However, no one ever talks about what colour eyes they have, because the monks have a vow of silence. Also, there are no reflective surfaces on the whole island. Thus, no one knows their own eye colour; they can only see the eye colours of other people, and not say anything about them. Life goes on, with brown-eyed monks and red-eyed monks living happily together in peace, and no one ever committing suicide. Then one day a tourist visits the island monastery, and, not knowing that he’s not supposed to talk about eyes, he states the observation “At least one of you has red eyes.” Having acquired this new information, something dramatic happens among the monks. What happens?

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  • draw a square. divide it into four identical squares. remove the bottom left hand square. now divide the resulting shape into four identical shapes.

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  • An old farmer died and left 17 cows to his three sons. In his will, the farmer stated that his oldest son should get 1/2, his middle son should get 1/3, and his youngest son should get 1/9 of all the cows. The sons, who did not want to end up with half cows, sat for days trying to figure out how many cows each of them should get.

    One day, their relative came by to see how they were doing after their father’s death. The three sons told him their problem. After thinking for a while, the relative said: “I’ll be right back!” He went away, and when he came back, the three sons could divide the cows according to their father’s will, and in such a way, that each of them got a whole number of cows.

    What was the relative’s solution?

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  • Two Egyptian camel drivers were fighting for the hand of the daughter of the sheikh of Arab. The sheikh, who liked neither of these men to become the future husband of his daughter, came up with a clever plan: a race would determine who of the two men would be allowed to marry his daughter. Therefore, the sheikh organised a camel race. Both camel drivers had to travel from Cairo to Abbudzjabbu, and the one whose camel would arrive last in Abbudzjabbu, would be allowed to marry the sheikh’s daughter.
    The two camel drivers, realising that this could become a rather lengthy expedition, finally decided to consult the Wise Man of their village. Arrived there, they explained him the situation, upon which the Wise Man raised his cane and spoke four wise words. Relieved, the two camel drivers left his tent: they were ready for the contest!

    Which four wise words did the Wise Man speak?

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  • Consider a grid of size 4 by 4 (i.e. sixteen squares), where all squares should get a colour. The coloured grid should meet the following conditions:

    4 squares should be coloured blue,
    3 squares should be coloured red,
    3 squares should be coloured white,
    3 squares should be coloured green,
    3 squares should be coloured yellow, and
    no colour may appear more than once in any horizontal, vertical, or diagonal line.

    How can the grid be coloured?

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  • Of all the numbers whose literal representations in capital letters consists only of straight-line segments (for example, FIVE), only one number has a value equal to the number of segments used to write it.

    Which number has this property?

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  • Mice can multiply very fast. Adult mice can give birth once every month, and baby mice grow into adult mice in just two months after they are born.

    If you would buy a baby mouse just after it was born, how many mice would you have in 10 months?

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  • You are sitting with one opponent at an empty, round table. Taking turns, you should place one euro on the table, in such a way that it touches none of the coins that are already on the table. The first player that is not able to place a euro on the table has lost. By tossing a coin, it has been decided that you may start.

    Which strategy will you follow to make sure you are guaranteed to win?

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  • On a geography test you have to tell which of two German cities is greater in population for all possible pairs of the 80 largest cities of Germany. (And that’s the only task on the test since it’s already 5 pages long.) But you didn’t study last night, and only even recognise half the cities, and don’t even know how those are ordered relative to each other. Your friend on the other hand studied dutifully all night and recognises all the cities and even knows how two cities are ranked relative to each other 60% of the time.

    A week later you get the test-result and you have a higher score than your friend. How come?

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  • What is the least number of links you can cut in a chain of 21 links to be able to give someone all possible number of links up to 21?

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