sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 29, 2006 17:13:21 GMT -5
Post by sublime on Nov 29, 2006 17:13:21 GMT -5
Some kids at school have been thinking about this for two days and still haven't gotten. It is possible, just requires some thinking.
You have two ropes of equal lengths and an infinite supply of matches. It takes each rope exactly one hour to burn from one end to the other. The ropes do not burn evenly, meaning, half the rope does not necessarily burn in thirty minutes. Using just the two ropes and the matches, measure forty-five minutes.
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Riddle
Nov 29, 2006 21:48:01 GMT -5
Post by TheJay on Nov 29, 2006 21:48:01 GMT -5
Well, I have a theory but I'm not sure it's the "correct" answer.
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sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 29, 2006 21:50:07 GMT -5
Post by sublime on Nov 29, 2006 21:50:07 GMT -5
post it...doesn't hurt to make a guess..i didn't make this up, but i've heard some stupid guesses on this lol. so don't think it's make you sound dumb
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Riddle
Nov 29, 2006 21:52:52 GMT -5
Post by TheJay on Nov 29, 2006 21:52:52 GMT -5
Well, though the ropes don't burn evenly, it takes an hour to burn completely. So my guess is you start burning one at both ends so that it burns twice as fast as normal. It'll take 30 minutes because even if one side burns slower than the other, the other flame will make up for it. Similarly, if you light the other rope in 4 equidistant places once the first burns, it should take 15 minutes.
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sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 29, 2006 22:01:18 GMT -5
Post by sublime on Nov 29, 2006 22:01:18 GMT -5
Well, you're first part is right on how you would get thirty minutes. The only problem with you second part is that you would have no wya to measure the distance to make them equidistant. I actually wasn't expecting that answer, but it seems to work if you could make sure they were equidistant. There's a different way I was looking for though.
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Riddle
Nov 29, 2006 22:08:08 GMT -5
Post by TheJay on Nov 29, 2006 22:08:08 GMT -5
Yeah, the second rope was the part I wasn't sure of. I guess you could keep lighting matches one after another while the first rope burns and keep track of how many it takes. When it's done burning, burn half as many matches as it took to burn in 30 minutes. That seems about as infeasible as my original idea though, given the time it would take to light each match. I'm glad to know I got the 30 minutes part right.
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sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 29, 2006 22:13:09 GMT -5
Post by sublime on Nov 29, 2006 22:13:09 GMT -5
Nah that's not right. The second part's harder harder to get.
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Riddle
Nov 30, 2006 20:46:08 GMT -5
Post by TheJay on Nov 30, 2006 20:46:08 GMT -5
Light one end of the second rope as you light both ends of the first rope. Then after the first rope is completely burnt, there's 30 minutes of burning time left on the second rope. Lighting the other end of the second rope at that point cuts that time to 15 minutes by the same logic that says the first rope will burn in 30 minutes. So 30 minutes of the first rope plus 15 minutes of the second rope yields 45 minutes.
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sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 30, 2006 20:48:51 GMT -5
Post by sublime on Nov 30, 2006 20:48:51 GMT -5
exactly.
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Riddle
Nov 30, 2006 20:51:36 GMT -5
Post by TheJay on Nov 30, 2006 20:51:36 GMT -5
Cool, it was a good riddle. I think I'm going to steal this and foist it on people.
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sublime
Graduating Newbie
[M:300000]
Posts: 150
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Riddle
Nov 30, 2006 21:06:01 GMT -5
Post by sublime on Nov 30, 2006 21:06:01 GMT -5
go right ahead, it makes people crazy
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Riddle
Nov 30, 2006 21:12:10 GMT -5
Post by TheJay on Nov 30, 2006 21:12:10 GMT -5
Then tell people after they solve it that the ropes were your only way down from Devils Tower.
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