Hourglasses 2 - Solution

Puzzles -> Measuring Puzzles

The Puzzle: An eccentric professor used a unique way to measure time for a test lasting 15 minutes.

He used just two hourglasses. One measured 7 minutes and the other 11 minutes.

During the whole time he turned the hourglasses only 3 times.

How did he measure the 15 minutes?

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The Solution . . .

When the test began, the professor started both hourglasses running.

When the 7min hourglass ran out, he turned it around.

4 minutes later, the 11min hourglass ran out, and he promptly turned the 7min hourglass around again, so the 4 min ran back again.

11+4=15, and the test was over.

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