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| quote: | You have 12 steel balls. All of them look totally equil. But one of them is defect. It's either lighter, either heavier then the rest balls - no one knows!
We have scales, that can show only: left pan is heavier, right pan is heavier, their weight is equil.
You have to find defect ball and tell wether it's heavier/lighter IN 3 WEIGHING!!
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Here's the answer:
1)Devide all balls into 3 groups - 4 balls in each - 1, 2 and 3
2)First weighing: we compare 1 Vs. 2 group - this weighing will tell wich group is lighter (if defect ball in third group solution is obvious)
3)Second weighing: on EACH scale's pan we put TWO balls from lighter group and also one ball form heavier group (3 balls Vs. 3 balls)
After weighing defect ball is either among two balls (from lighter group) on lighter pan or either in one ball (from heavier group) on heavier pan.
4)Last, third weighing - compare two light balls.
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