I'm not sure how well known this problem is but it's one of my favourites.

You have 12 snooker balls. 11 of them weigh exactly the same. One is either heavier or lighter than the others.

The only way you can determine which ball is different is to use a balance scale with two pans - on which you can weigh any number of balls on either side. The scale will only tell you which pan is heavier or if they are both equal.

You need to determine which ball is different and whether it is heavier or lighter than the others.

What is the minimum number of weighings you need to achieve this?

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