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[I saw this one quoted above, but couldn' see the solution--sorry if this is a repeat]
6. Eight billiard balls: Only weigh six of the balls, 3 on each side. If one of the sides is heavier than the other, you weigh 2 of those balls. If one of the 2 is heavier, you have your answer. If not, then you know the 3rd ball is the heavier ball. If the original 6 balls you weighed balance, then the heavier ball is one of the 2 you didn't weigh. Weigh those 2 balls, and the heavier is the defective. I hope that makes sense.
My favorite brain-teazer is something like this: You find two light switches outside a room, and 3 lightbuls inside the room. You need to determine which switch controls which bulb, but you can only flip each swich on and off one time, and you can only go inside the room once.
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