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        riddles >> medium >> Burnt out Fuse
        
(Message started by: melimel on Dec 3^rd, 2006, 6:26am)

Title: Burnt out Fuse
Post by melimel on Dec 3^rd, 2006, 6:26am

You have 2 fuses , each 12" long. Each fuse burns in exactly one hour, but does not necessarily burn at a uniform rate. Also, thee are two fuses dont necessarily burn at the same rate over corresponding segments. But a given segement on a given fuse burns in the same amount of time in either direction. How do you use these 2 fuses to time 15 minutes? How do you time 15 minutes only using 1 fuse ??? ???

Title: Re: Burnt out Fuse
Post by towr on Dec 3^rd, 2006, 8:34am

Light three ends, and keep at least two burning.

Title: Re: Burnt out Fuse
Post by melimel on Dec 4^th, 2006, 4:54pm

thats works if you can use 2 fuses BUT how do you figure 15 min if you only use 1 fuse???? ???

Title: Re: Burnt out Fuse
Post by Noke Lieu on Dec 4^th, 2006, 9:00pm

Well, it could be a trick question in that you use one fuse up to get 15 minutes on the other fuse... for example, two fuses A and B.
Sacrifce A to leave you with a 30 (or 15) minute fuse B'.

When A extinguishes (from lack of fuel), extinguish B' and save it until you want to time 15 minutes. That'd be only one fuse.

Title: Re: Burnt out Fuse
Post by rmsgrey on Dec 5^th, 2006, 7:59am

It's just about possible to do with a single fuse - assuming you're very quick at igniting things - light the fuse at each end and somewhere in the middle. Whenever a piece burns out, light the remaining piece somewhere in the middle. Since you have 4 ends burning at any given moment, you'll consume the entire fuse in 15 minutes.