Puzzles

Can You Solve the Hourglass Logic Puzzle?

The hourglass brain teaser is a classic logic puzzle in that it requires little math skills—just some logical, practical thinking. This logic problem is featured in the book "Fundrum My Conundrum: A Book of Riddles" by Raymond Epstein and Benjamin Kovler. Give this problem a shot before scrolling down to read the solution. Good luck!

Here's The Logic Puzzle

You have two hourglasses—one hourglass measures 7 minutes, and the other hourglass measures 4 minutes. How can you time 9 minutes using nothing but these two hourglasses? Yes, this is possible! Scroll down to read the solution.

Here's the Answer

Start both hourglasses at the same time. When the four-minute hourglass runs out, turn it over to start it again (four minutes have elapsed at this point). When the seven-minute hourglass runs out, turn it over to start it again (at this point, seven minutes total have elapsed). When the four-minute hourglass runs out for the second time, eight minutes have elapsed. At this time, the seven-minute hourglass has been running for one minute. Turn the seven-minute hourglass over again and wait for the one-minute's worth of sand to run out. Once that hourglass runs out, nine minutes will have elapsed.

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Written by Curiosity Staff March 15, 2017