• Brain Teasers & Puzzles

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    • There are three Federation Officers assigned to take three hostile aliens to “Peace Talks” on another planet. However, they must follow the following rules:

      They have only one small space ship.
      Only two individuals can ride in the space ship each time.
      All Federation Officers can pilot the space ship, but only one alien can pilot the ship.
      If at any time there are both Federation Officers and aliens on a planet, then there must always be more (or the same number of) Federation Officers than aliens on that planet. This is because if there are more aliens than Federation Officers, then the aliens will kill the Federation Officers. Count any individual in the space ship when it is on one planet as being on that planet.
      The one space ship is the only means of transportation. There is no other way to get to the “Peace Talks”. No one can exit the space ship while it is in flight.
      To start off, all the Federation Officers and aliens are on the same planet.

      Can all Federation Officers and aliens get to the other planet alive, and if so: how?

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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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    • Mr. Dutch, Mr. English, Mr. Painter, and Mr. Writer are all teachers at the same school. Each teacher teaches two different subjects. Furthermore:

      three teachers teach Dutch language;
      there is only one maths teacher;
      there are two teachers for chemistry;
      two teachers, Simon and Mr. English, teach history;
      Peter does not teach Dutch language;
      Steven is chemistry teacher;
      Mr. Dutch does not teach any course that is taught by Karl or Mr. Painter.

      What is the full name of each teacher and which two subjects does each one teach?

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    • Consider a list of 2000 statements:

      1) Exactly one statement on this list is false.
      2) Exactly two statements on this list are false.
      3) Exactly three statements on this list are false.
      . . .
      2000) Exactly 2000 statements on this list are false.
      Which statements are true and which are false?

      What happens if you replace “exactly” with “at least”?

      What happens if you replace “exactly” with “at most”?

      What happens in all three cases if you replace “false” with “true”?

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    • Vicky caught four animals in the Great Animal Forest and put them into four separate cages. The four animals are:

      the lion, that always tells the truth;
      the jackal, that always lies;
      the parrot, that always repeats the last given answer (if he is the first one, he randomly says “yes” or “no”);
      the giraffe, that is so slow that he always truthfully answers the previous question (if he is the first one, he also randomly says “yes” or “no”).
      The other animals want to free them and send the small, smart hedgehog on the way to size up the situation. In the middle of the night, the hedgehog creeps into the camp of the Vicky and tries to figure out which animal sits in which cage. One by one, he asks them “are you the jackal?” After hearing the four answers, the hedgehog only knows in which cage the giraffe sits. Then the hedgehog asks them in the same order “are you the giraffe?” After hearing the four answers, the hedgehog also knows in which cage the jackal sits. Because the hedgehog then still does not know in which cages all animals sit, he asks the first animal “are you the parrot?” The answer is “yes”, and now the hedgehog knows exactly which animal sits in which cage. The hedgehog returns to the other animals and together they free the captured animals.

      Which animal was in which cage?

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    • There is a rich man living with two other people his butler and his maid. One day the rich man is sitting at his desk counting his money, preparing to deposit it at the bank. When he is done he goes to the bank, but when he arrives, he realises he left a $100 dollar bill on the desk. So he quickly called the house and told the butler that he forgot the $100 bill on the desk, and he will come home now to pick it up. When he arrived home he asked the butler what he did with the bill, the butler said he put it under the green book on the desk. When the rich man looked under the book, it wasn’t there, so he asked the maid if she saw it. She said she saw the $100 bill when she was dusting and put it between pages 67 and 68 of the green book. Right then and there the rich man called the police, and knew who stole it, even before the rich man checked inside the book to see if the $100 bill was there. How did he know?

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    • Here you see a pool with six happy frogs. You must exchange the positions of the brown and green frogs, using the following rules:

      a frog can only jump to an empty water lily;
      a frog can only jump over at most one other frog, that has another color;
      a frog can only jump forward (so the green frogs jump right and the brown frogs jump left).

      How can this be done?

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    • Assuming year 1 started on Sunday, it can be shown that only some days are possible as a century’s final day. What are these days?

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    • There is a tree 20 feet high, with a circumference of 3 feet. A vine starts at the base of the tree and winds around the tree 7 times before reaching the top. How long is the vine?

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    • Four men want to cross a bridge. They all begin on the same side. It is night and they have only one flashlight with them. At most two men can cross the bridge at a time and any party who crosses, either one or two people, must have the flashlight with them. The flashlight must be walked back and forth: it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the speed of the slower man. Man 1 needs 1 minute to cross the bridge, man 2 needs 2 minutes, man 3 needs 5 minutes, and man 4 needs 10 minutes. For example, if man 1 and man 3 walk across together, they need 5 minutes.

      How can all four men cross the bridge in 17 minutes?

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