12 weights, one is different

James Lambert · 2015-12-02T09:48:46

Somebody told me a puzzle I really liked. It took me a few hours to figure out 90% of it and didn't figure it out completely until the next day. Nobody who I have asked this puzzle to has been able to figure it out. You have 12 weights that look identical but one weighs more or less than the others. You don't know if it weights more or less, just that the weight is different. You have a balance scale you can only use three times. So you can place any number of weights on either side of the scale then look at the scale to see if it leans left, right or stays balanced. A single observation of the scale's balance with any configuration of weights counts as a use. You need to find out which weight is different and if it weighs more or less than the rest only using the scale 3 times. Can you do it?