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Old 10-22-2010   #1 (permalink)
aŮejo
 
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Question Two Strings

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?


EDIT: You may have noticed this thread was closed as soon as it was created. That was not intended to limit your input or enjoyment in any way. On the contrary, your participation is most welcome. The action was taken to prevent eager Peeps from going into some search engine, finding the answer, and posting it, as happened on several occasions in the past. (Of course I harvest a lot of this material from other sources. You didnít think I create it all myself, did you? Iím good, but Iím not that good!) Regrettably, that also means that folks who legitimately work out their own answers, and would like to post them, donít get to display their prowess, but Iím afraid that canít be helped. Iíll open the thread in a couple of days, when Peeps have had an opportunity to try their hand at a solution, and you can post away then. The official answer will come a bit after that. I appreciate your patience and understanding, and hope you enjoy the exercise.
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Old 10-27-2010   #2 (permalink)
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Take your best shots. This one is a little tougher.
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Old 10-31-2010   #3 (permalink)
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The Official Answer

Light both the ends of the first string and one end of the second string. 30 minutes will have passed when the first string is fully burned, which means 30 minutes have burned off the second string. Light the end of the second string and when it is fully burned, 45 minutes will have passed.

Some people have difficulty grasping that when you light both ends of the first fuse, it will take 30 minutes to burn. Because the burning rate is random and unknown to you, you have no idea where the 30 minute mark is on the fuse. If you had an exact duplicate, then the 30 minute mark would be in the same place. It is probably not in the middle, but it is somewhere. If you burn both ends of a fuse it will not stop burning until it has reached this mark, which means 30 minutes is up.
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Old 11-01-2010   #4 (permalink)
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Wouldn't it be better to just extinguish the string after it burned 3/4 of the way?

Then save the other string for the next time you have time something?

Burning an hour and 15 minutes worth of string for a 45 minute timer is just plain string abuse.
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Old 11-01-2010   #5 (permalink)
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Two strings walk into a bar...
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Old 11-01-2010   #6 (permalink)
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I thought this was another swimsuit fashion thread.
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Old 11-01-2010   #7 (permalink)
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Quote:
Originally Posted by UnoMasMezcal View Post
Wouldn't it be better to just extinguish the string after it burned 3/4 of the way?

Then save the other string for the next time you have time something?
Ah, but it says the burning rate is completely random, so you couldn't be certain burning 3/4 of the string was necessarily 3/4 of the time.

Quote:
Originally Posted by UnoMasMezcal
Burning an hour and 15 minutes worth of string for a 45 minute timer is just plain string abuse.
You gonna' report me to the string police? I think they're a division of that bunch that checks up to see if you take the labels off the pillows and mattresses.

Last edited by Bumper; 11-02-2010 at 05:38 AM..
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