May 20, 2002
Problem of the Month

Hard Boiled
by Karl Fulves

With a 7-minute hourglass and an 11-minute hourglass, what is the quickest way to time the boiling of an egg for 15 minutes?

Solution to the Problem:

There are several ways to boil the egg with the two timers but the quickest is 15 minutes.

To do this, turn over both timers and start boiling the egg.

When the 7-minute timer is finished, turn it over.

When the 11-minute timer is done, four minutes worth of sand has drained from the 7-minute timer.

So, turn over the 7-minute timer.

When the 7-minute timer is finished, 15 minutes will have elapsed, so take the egg off the stove.

Correctly solved by:

1. Kelsey Dufendach	Rockford, Michigan
2. Walt Arrison	Philadelphia, Pennsylvania
3. David L. Stark	Winchester, Virginia
4. Keath Mealy	Cincinnati, Ohio
5. Nate Troup	Arlington, Virginia
6. Rick Jones	Kennett Square, Pennsylvania
7. Geoff Keith	Santa Monica, California
8. David Powell	Winchester, Virginia
9. John Funk	Ventura, California
10. Bill Hall	Wellington, Florida
11. James Alarie	University of Michigan -- Flint, Michigan
12. David and Judy Dixon	Bennettsville, South Carolina

Send any comments or questions to: David Pleacher