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My 1st puzzle post

  1. Nov 16, 2005 #1
    posting my 1st brainteaser ...hopefully u might enjoy

    uve got 20 blue balls and 14 red balls all mixed up ( u also have some spare balls outside the box) in a box u have to take out 2 balls at a time. if they r the same leave them outside of the box and put in a blue spare (the spares r not diffirent in any way to the ones in side already ).if they r diffirent put red back in box leave blue out.......question if u keep taking balls out will the last ball always be the same colour ,,if yes wat colour?

    a proper detailed answer plz

    for those who like creative thinking puzzles.....
    What is " never odd or even " ?
  2. jcsd
  3. Nov 16, 2005 #2
    Code (Text):

    choice  blue result  red result
    b b         -1           0
    r r         +1          -2
    b r         -1           0
    r b         -1           0
    Note that after each trial there is one fewer ball in the box than before. So after 33 trials there will be just one ball left in the box.

    Reds are only ever removed 2 at a time, and never added, so the number of reds in the box must remain even.

    Therefore the last ball in the box after 33 turns will always be blue.
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