Saturday, November 20, 2010

How to measure 16 minutes using 2 hourglasses?

John has a small and a large hourglasses. The small one can measure 5 minutes and the large one can measure 7 minutes. How can he measure 16 minutes with 2 hourglasses running together?

The rule is when any one of the hourglasses finishes leaking, that hourglass must be flipped over immediately to keep it running.

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