Math is Fun

Math is Fun Home PageHOME

A-Z Listing


Top-rated teacher Web sites rated by teacher usage
Edunet site of the week January 2001
Maths Is Fun is ICRA Registered
Copyright © 2006
MathsIsFun.com

Hourglasses 2 - Solution

Puzzles -> Measuring Puzzles

Hourglasses 2The 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?


.
.
.
.
(Scroll down if you really want
to see the Solution ...)

.
.
.
.
.
.

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.


Discuss this puzzle at our Forum