November 23, 2006
Rope Brain Teaser

How are your logic solving skills? The Rope burning logic problem was posted up on and I haven't the slightest idea where to start. You guys?

Posted by Arcterex at November 23, 2006 08:54 AM

Easy, start one of the rope by both ends and at the same time start one end of the second rope. When the first rope finish burning (30 minutes), start the second end on the second rope. It will takes an extra 15 minutes to burn the second rope :)

Posted by: Eric on November 23, 2006 10:19 AM

Fold 1st rope in two to find middle. Start 1st rope on both ends and in the middle. Start second rope. When 1st rope is consumed there will be 45min left on 2nd rope.

Posted by: Mu on November 23, 2006 12:43 PM

Mu, your solution is incorrect.
Lets say the half of the first rope burns in seconds and the other half is burning almost whole hour.
So in your situation when the first rope is lighted on both ends and in the middle, one half burns immediately and the other half burns almost half an hour.
In this case there is only about 30min left on the second rope.

Posted by: Domas on November 24, 2006 2:52 PM

The answer is watch the time on your computer. You said that you gave me a lighter and two ropes period nothing else then you said THIS (meaning my computer) is the only equipment I can use.
There for watch the clock.

Posted by: Brandon on November 25, 2006 10:22 AM

How about this idea.. Fold rope 1 in 1/2 to determine the center. Straighten it out and light the middle and both ends of rope 1. This starts rope 1 burning in 4 different directions, reducing the entire time for rope 1 to be consumed to 15 minutes (1/4 of 60min). At the same time, light one end of rope 2. When rope one is completely consumed, start your timer. Rope 2 should be finished 45 minutes later.

Posted by: mike on November 25, 2006 5:30 PM

fill the lighter with fluid. light one rope, and keep the lighter lit. after one hour, measure the amount of fluid consumed. multiply that by .75, and fill the lighter with the calculated amount. if you then continuously burn the lighter, it will burn for 45 minutes, assuming no other conditions have changed.

Posted by: ed on November 27, 2006 6:19 AM

A solution has been posted on the site.

Posted by: Arcterex on November 27, 2006 9:59 AM
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