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Here's another riddle

  1. May 21, 2013 #1
    You are given eight coins of same denomination, out of the eight coins one coin is very very slightly heavy than the remaining seven such that you cannot separate it by weighing it in your palms. You are given a beam balance with the help of which you have to separate out the very slightly heavy coin but you are allowed to use the balance only twice.
     
  2. jcsd
  3. May 21, 2013 #2
    There's probably a better way to word this but here is my solution.

    Put 3 on one side, 3 on the other. If the scale doesn't tip, weigh the 2 that were not on the scale.

    If one of the 3 tips, pick 2 of those and put them on the scale, if it balances it's the 3rd one of that group if not the scale will tip.
     
  4. May 21, 2013 #3
    absolutely correct :approve:
     
  5. May 22, 2013 #4

    mfb

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    2016 Award

    Staff: Mentor

    You can do the same with 9 coins.
    Or, in general, with 3n coins if you can use the balance n times.
     
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