You are a cook in a remote area with no clocks or other way of keeping time other than a four minute sandglass timer and a seven minute sandglass timer. (The kind you turn over – hourglass shaped) You do have a stove, however, with water in a pot already boiling. Somebody asks you for a nine-minute egg, and you know this person is a perfectionist and will be able to tell if you undercook or overcook the eggs by even a few seconds. What is the least amount of time it will take to prepare the egg? And how will you prepare it so that it is neither undercooked or overcooked?
Happy Thanksgiving from The RiddleDude
November 24th, 2011 | Category: 
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T4 is the 4 minutes timer
T7 is the 7 minutes timer
1- Turn them both
2- Once T4 ends, T7 has 3 minutes to go, turn T4 around
3- Once T7 ends, T4 has 1 minute to go, turn T7 around
4- Once T4 ends, T7 has 6 minutes to go, now turn them BOTH around
5- Once T4 ends, T7 has 2 minutes to go, now put the egg in the boiling water
6- once T7 ends, turn it around again and wait for it to end then remove the egg (Cooking time 9 minutes)
So how long did this take?
2- 4 minutes passed
3- 3 minutes passed
4- 1 minute passed
5- 4 minutes passed
6- 9 minutes cooking time
= 21 minutes including cooking time…
Now the really complicated part is trying to explain to the perfectionist customer that he’s gonna have to wait 21 minutes for a 9 minutes boiled egg :)
Nine minutes is correct!
First, flip both hourglasses over and drop the egg into the water. When the four minute timer runs out, flip it again. When the seven minute timer runs out, flip it over. The egg has been cooking seven minutes. Now when the four minute timer runs out again (after eight minutes) flip the seven minute timer back over. Since the seven minute timer has been running only a minute between flips, there’s a minute worth of sand left. And when that minute runs out, the egg will have been cooking for exactly nine minutes.
You’re today’s winner, Rool.
FYI: I had it wrong, and I stand corrected…
Thanks dude