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Weighing marbles

  1. Apr 1, 2007 #1
    i give you 12 marbles. 11 of them are identical. the 12th one looks the same, but is either heavier or lighter than the other 11.

    you also have a balance scale. the kind that weighs things on both sides - and if one side is heavier, it tilts down.

    you are allowed only 3 weighings.

    tell me which ball is the oddball, and whether it is heavy or light.
  2. jcsd
  3. Apr 1, 2007 #2
    This was just posted one or two months ago. In fact, a search for "balance" in the Brain Teasers forum shows that it is posted quite frequently. I wonder what it is about this particular puzzle that makes it so popular.
  4. Apr 1, 2007 #3
    sorry about that. i did look thru the first page for marbles, and did not see anything. i didnt look more closely at the rest of the wording.

    to answer your question - it took me a long time to figure it out. it has been one of the best puzzles that i have worked on for a long time.
  5. Apr 1, 2007 #4
    i was just about to post the one about crossing the river with cannibals, but i find that this has also been posted. it only took me an hour or so to figure that one out. i found the marble one much more difficult.
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