Be a science detective - test of problem-solving skills #1

Adapted with permission from Professor Daryl Cooper, Department of Mathematics, University of California at Santa Barbara.
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Picture 12 balls that look identical. One of the balls is either heavier or lighter than the others. If I give you a balance and allow you to make three weighings, how would you go about discovering which ball is the odd one out, and whether it is heavier or lighter than the others?

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Click here for a clue.

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