Tennis Ball Weighing Problem

80. Tennis Ball Weighing Problem

You have 12 tennis balls, 1 is heavier or lighter than the rest. You get 3 weighings with a balance beam scale. After the third weighing, you have to be able to tell me which ball and if it's heavier or lighter.

Added 23 January 2009

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Solution:

First, divide the 12 balls into three groups of four. Weigh two groups against each other. Depending on the outcome, you will know if the odd ball is in one of those groups or in the group not weighed. Continue to narrow it down using the balance scale until you identify the odd ball and determine if it is heavier or lighter.

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