holystove Posted April 12, 2010 Report Share Posted April 12, 2010 Took me a while to figure this out but an enjoyable riddle nonetheless : There's two separate pieces of rope of equal length. If you light one end of the rope on fire, it takes 1 hour for the fire to reach the other end of the rope. However if the fire has burnt half the rope, that doesn't mean that half an hour has passed, so you can't deduce anything from that. Sometimes the rope burns faster, sometimes slower, all you know is that it takes 1 hour for the fire to go from one end to the other. Now, you have the two pieces of rope and a lighter. You have no clock but how can you know when 45 minutes have gone by after you've first set fire to one (or both) of the ropes? Quote Link to comment Share on other sites More sharing options...
The Beard Posted April 12, 2010 Report Share Posted April 12, 2010 I have started musing on this one. Not solved it yet but I am looking on the lines of setting both ends alight, presuming that would take 30 mins. Still looking to sort out the remaining 15 minutes OR I am completely on the wrong track Quote Link to comment Share on other sites More sharing options...
holystove Posted April 12, 2010 Author Report Share Posted April 12, 2010 I have started musing on this one. Not solved it yet but I am looking on the lines of setting both ends alight, presuming that would take 30 mins. Still looking to sort out the remaining 15 minutes OR I am completely on the wrong track You're right there. Impressive how quickly you figured out the first step. Second step should be easy for you now. Quote Link to comment Share on other sites More sharing options...
Matt Posted April 12, 2010 Report Share Posted April 12, 2010 (edited) right, im putting this down to the 3 hours kip and 4:30am start, but i googled various answers to this admn thing and none of them make sense!!! I went with Beards idea, and the answers i found from google, but since you know that the rope burns at quicker and slower at random times, how does lighting it at both ends give you a better idea of how quickly it burns? Edited April 12, 2010 by galacticaracnid Quote Link to comment Share on other sites More sharing options...
holystove Posted April 12, 2010 Author Report Share Posted April 12, 2010 how does lighting it at both ends give you a better idea of how quickly it burns? Well The Beard figured out that if you set fire at both ends of a rope, logically it will be gone in 30 minutes instead of 1 hour. Now all he has to do is figure out how to get the last 15 minutes. Doesn't really matter how quickly it burns. All you need to know is, each rope takes 1 hour to burn from one end to the other. Quote Link to comment Share on other sites More sharing options...
MikeO Posted April 12, 2010 Report Share Posted April 12, 2010 Got it....but only by cheating (it was annoying me) . So I won't post the answer. Quote Link to comment Share on other sites More sharing options...
Matt Posted April 12, 2010 Report Share Posted April 12, 2010 Well The Beard figured out that if you set fire at both ends of a rope, logically it will be gone in 30 minutes instead of 1 hour. Now all he has to do is figure out how to get the last 15 minutes. Doesn't really matter how quickly it burns. All you need to know is, each rope takes 1 hour to burn from one end to the other. ive got a good arguement as to why it does matter but im too tired and my taxi to the hotel is coming in a min! Good puzzle though, thank you for making me feel completely retarded Quote Link to comment Share on other sites More sharing options...
iggy Posted April 13, 2010 Report Share Posted April 13, 2010 (edited) I know this one from a recent quiz night so will let the rest of you fight it out! Edited April 13, 2010 by iggy Quote Link to comment Share on other sites More sharing options...
marcopaulo Posted April 13, 2010 Report Share Posted April 13, 2010 figured it out using the first bit provided by beard... light both ends of one and that will take half hour to burn fully... light one end of the other rope at the beginning too..when the first rope is burnt out light the other end of the second rope and it should be 45 minutes total when it fully burns..presuming it is 30 mins for half the rope with 1 end lit and 15 mins for the other half with 2 ends lit... Quote Link to comment Share on other sites More sharing options...
marcopaulo Posted April 13, 2010 Report Share Posted April 13, 2010 ive got a good arguement as to why it does matter but im too tired and my taxi to the hotel is coming in a min! Good puzzle though, thank you for making me feel completely retarded i dont get why it matters? they only put it as 1 hour so you have the time figured out and saying it burns quicker or slower so that you cant cut one rope in half i guess! all for the purpose of the puzzle but doesnt make sense in the real world if thats what you meant Quote Link to comment Share on other sites More sharing options...
holystove Posted April 13, 2010 Author Report Share Posted April 13, 2010 figured it out using the first bit provided by beard... light both ends of one and that will take half hour to burn fully... light one end of the other rope at the beginning too..when the first rope is burnt out light the other end of the second rope and it should be 45 minutes total when it fully burns..presuming it is 30 mins for half the rope with 1 end lit and 15 mins for the other half with 2 ends lit... Correct . Quote Link to comment Share on other sites More sharing options...
The Beard Posted April 13, 2010 Report Share Posted April 13, 2010 (edited) You're right there. Impressive how quickly you figured out the first step. Second step should be easy for you now. Ok, I haven't checked any other answers but if I apply the same principle to the first one but start burning one end only, of the second rope, that is 30 minutes gone so if I then light the other end it should take another 15 minutes making 45 minutes. Doesn't look right but only thin I can come up with. Edited April 13, 2010 by The Beard Quote Link to comment Share on other sites More sharing options...
holystove Posted April 13, 2010 Author Report Share Posted April 13, 2010 Ok, I haven't checked any other answers but if I apply the same principle to the first one but start burning one end only, of the second rope, that is 30 minutes gone so if I then light the other end it should take another 15 minutes making 45 minutes. Doesn't look right but only thin I can come up with. That the correct solution. Why doesn't it look right? Quote Link to comment Share on other sites More sharing options...
The Beard Posted April 13, 2010 Report Share Posted April 13, 2010 That the correct solution. Why doesn't it look right? Maybe it was the way I explained it, thre me However, I have just done it hypothetically or should that be pathetically and now realise, that the second will burn in 15 minutes as it has already been burning for 30 minutes so will only have half to burn through at twice the speed, hence 30+15=45 minutes Quote Link to comment Share on other sites More sharing options...
rubecula Posted July 16, 2010 Report Share Posted July 16, 2010 First rope light at both ends, after thirty minutes when it has burned away, you light the second rope at both ends AND the middle, this should take 15 mins. 30 mins for first rope plus 15 for second equals 45 mins. Umm Is that right without looking at the "Spoiler"? Quote Link to comment Share on other sites More sharing options...
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