Problem:

You have 8 balls of equal size. 7 of them weigh the same, and one is slightly heavier. You can use a balance scale but only twice. How do you find the heavier ball?

Scroll to the bottom of the page for the answer

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Solution:

Divide the balls into three groups (3-3-2). Weigh the first two groups of three against each other. If they balance, the heavier ball is in the last group of two—weigh them to find the heavier one. If they don't balance, weigh two balls from the heavier group. If they balance, the third ball is the heavier one.