- Jul 29, 2001
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Whoever correctly answers this problem gets to post the next (and gets respect).
Everyone knows the classic 9-marble-and-one-is-heavier problem. You have 9 marbles, one is heavier than the rest, and a balance. How do you find the heavy one with 2 weighs?
The answer is to split the marbles into 3 groups of 3. Weigh group A vs group B. The heavy ball will be in the heavy group if one is heavier than the other. If they are the same, you know the heavy marble is in group C. Pick any two marbles from the heavy group and weigh them. Apply the same logic as to the groups in order to determine which is the heavy ball.
Too simple? Well here ya go:
You have a balance and 12 marbles, 11 of which are of the same weight. The other marble may be lighter or heavier than the rest, but you do not know which. Is it possible for you to point out the deviating marble AND tell whether it is lighter or heavier than the rest using only 3 weighs? If your answer is yes, you must provide a method which will always work. If your answer is no, you must prove that you will require at least 4 weighs.
Everyone knows the classic 9-marble-and-one-is-heavier problem. You have 9 marbles, one is heavier than the rest, and a balance. How do you find the heavy one with 2 weighs?
The answer is to split the marbles into 3 groups of 3. Weigh group A vs group B. The heavy ball will be in the heavy group if one is heavier than the other. If they are the same, you know the heavy marble is in group C. Pick any two marbles from the heavy group and weigh them. Apply the same logic as to the groups in order to determine which is the heavy ball.
Too simple? Well here ya go:
You have a balance and 12 marbles, 11 of which are of the same weight. The other marble may be lighter or heavier than the rest, but you do not know which. Is it possible for you to point out the deviating marble AND tell whether it is lighter or heavier than the rest using only 3 weighs? If your answer is yes, you must provide a method which will always work. If your answer is no, you must prove that you will require at least 4 weighs.