Hi
I wanted to add my own friendly two-cent solution to the 15min egg problem.

At time0 start both timers, and begin to cook the egg.
At time7, timer7 expires- flip it over.
At time11, timer11 expires. Timer7 now has 3min of sand on top and 4min of sand on bottom. So flip over timer7!
At time15, timer7 expires. 15 minutes have passed.

Total of 2 flips. I agree that this doesn't (and can't) beat the one-flip solution, but it does allow the egg to be cooked given the cost of energy, and the fact that our need to purchase oil from other nations is a leading contributor to our nation's trade deficit problem!

However, given that this is the age of electronics, my solutions's drawback is that it TRULY requires 'hour-glasses'. That is, chronographs would not support my solution since it requires the device to count up as wellimmediately- not wait 7 minutes as Solution #3 requires. This of course is a big advantage as down at the same time. (the bottom sand is counting from 0 to 7 min, while the top sand is counting down from 7min to 0) Unless, the chronograph had both an up and down function, as many of today's Sport watches have; this is because sports clocks count time-remaining, not time-elapsed.

But of course, if you were using a watch, or equivelent, you would simply time 15 minutes directly! But that wouldn't make much a puzzle now either.

Hope you enjoyed my light-hearted and long-winded resolution.

John

Copyright © 1996-2008 Alexander Bogomolny

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