Sunday, May 25, 2008

Dragon and the Knight Puzzle

Dragon and the Knight Puzzle

A dragon and knight live on an island. This island has seven poisoned wells, numbered 1 to 7. If you drink from a well, you can only save yourself by drinking from a higher numbered well. Well 7 is located at the top of a high mountain, so only the dragon can reach it.

One day they decide that the island isn't big enough for the two of them, and they have a duel. Each of them brings a glass of water to the duel, they exchange glasses, and drink. After the duel, the knight lives and the dragon dies.

Why did the knight live? Why did the dragon die?



  1. well thats my approach to the answer....

    since both dragon and knight are enemies , they will try their best bet..

    so dragon bring a glass from 7th well to which their is no antidote...

    but now knight has trick ....

    before coming to the duel he drinks a glass from the 1st well...

    hence the glass from the 7th well given to him by dragon acts an antidote :-)

    now how does the dragon die ....
    dragon knows that knight can bring water from only 1-6 numbered wells
    so it can drink a glass from 7th well after the duel to neutralize the effect ....

    but knight is smart enough , he anticipates this and bring a glass of water from the SEA/OCEAN (after all they live on a island ;-) ) which is poison-less....

    dragon unaware of this fact still drinks a glass from 7th well and dies....

    hope thts justified and correct

  2. i agree with ur answer

  3. What if dragon is also smart enough to only bring water anticipating knight's trick. He only drinks water and since knight had drunk poison he dies. So it is not guaranteed that knight will always win with this strategy.

  4. I think dragon can never die if he is smart. The best that king can do is ensure that he also doesn't die. Before coming dragon drinks poison from well 6, and brings poison from well 7. Since no matter what king brings, he will always be poisonous after drinking king's glass and thus after drinking his own from well 7, he always survives. And now since this gives dragon 100% guarantee that he survives, king only has the option of drinking some poison before coming and bringing water for dragon, so that he gets neutralised by dragon's poison and then drinks his own water and he also survives.......what say ??

  5. But see both of you are trying to predict the outcome of a match between them; however, we already are given the outcome so what is left is to postulate how that ending came about. Dante's answer is the only possible one, so that by Occams Razor it must be the correct choice.

  6. I like Dante's solution but the wording of the puzzle does not exclude other solutions. The island many have several non-poisonous wells in addition to the poisonous ones. This makes sense if the two are to live on the island for any length of time. The availability of a non-poisonous well makes Dante's solution easier. There may well have been other poisons available (plants, snake or toad venom, mushrooms etc) for which there was no antidote and the knight could have poisoned the water with one of those. The dragon could also have died from wounds suffered in the duel.


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