Heavy or Light
You are given a set of weighing scales and 12 marbles. The scales are of the old balance variety. That is, a small dish hangs from each end of a rod that is balanced in the middle. The device enables you to conclude either that the contents of the dishes weight the same or that the dish that falls lower has heavier contents than the other. The 12 marbles appear to be identical. In fact, 11 of them are identical, and one is of a different weight. Your task is to identify the unusual marble and discard it. You are allowed to use the scales three times if you wish, but no more. Note that the unusual marble may be heavier or lighter than the others. You are asked to both identify it and determine whether it is heavy or light 
Keep 4 marbles in each sides of the scale
Case 1: If any of the two sides has unbalanced weight , then that side has unusual marble. So in that 4 keep 2 each sides and do the same procedure and any one side will be unbalanced . In those 2 keep again one each sides and one will be unbalanced. That will be the unusual marble. It has only 3 steps.
Case 2: If both of those 4 marbles are balanced,then again do the same procedure as mentioned above. This also has 3 steps. And the unusual marble is found.
Your Answer
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