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Faulty balls

  1. Jun 30, 2005 #1
    try this,
    there are eight bags. each bag contains 10 balls. one of those bags contains balls weighing 2 kg(all balls weigh the same). All the other balls weigh 1 kg. you have a weighing machine (not a balance). in one weighing u have to find out which bag contains the faulty balls.
  2. jcsd
  3. Jun 30, 2005 #2


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    I wouldn't be surprised if there are a lot of threads with problems like this one. This version is far too easy though. Just weigh any two bags. If they balance, then the third bag contains the faulty balls. If they don't balance, the heavier of the two contains them.
  4. Jun 30, 2005 #3


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    Nope, this is the one where you have a scale - rather than a balance so you weigh a different number of balls from each bag. (This is typically referrred to as the counterfit coin problem.)

    Vikasj007 graciously posted a more interesting version which involved 81 bags:
  5. Jun 30, 2005 #4


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    Oops. He even said "not a balance". Still, this one is too easy. Weigh two balls from bag A together with one ball from bag B. If the total weight is 3kg, then it's bag C, if the weight is 4 kg, then it's bag B, and if it's 5 kg then it's bag A.
  6. Jun 30, 2005 #5

    How do you keep missing that he said 8 Bags??? Its the first line for crying out loud... It still may be easy but at least read what he wrote...

    In white for anyone who doesent know the answer: Number the bags 1-8. Take 1 ball from bag 1, 2 from bag 2, exc.. Weigh the lot of them and subtract 34 from the answer... That is the bag number with the 2kg balls.

    EDIT: Thanks Everneo! I did mean 36 :rolleyes:
    Last edited by a moderator: Jul 1, 2005
  7. Jul 1, 2005 #6

    did you mean 'subtract 36' ?
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