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How to measure 45 minute by burning a fuse?

+2 votes
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You are provided two fuses. Each will burn for exactly one hour. But the fuses are not necessarily identical and do not burn at a constant rate. There are fast-burning sections and slow-burning sections. How do you measure forty-five minutes using only the fuses and a lighter?

posted Jan 13, 2014 by Vishvachi Tiwari

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1 Answer

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Best answer

At time zero, light both ends of fuse A and one end of fuse B. The fuses must not touch each other. It takes thirty minutes for fuse A's two flames to meet. When they do, there is exactly thirty minutes left on fuse B. Instantly light the other end of (still-burning) fuse B. The two flames will now meet in fifteen minutes, for an elapsed time of forty-five minutes.

answer Jan 13, 2014 by Atul Mishra



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You have a lighter and two fuses that take exactly one hour to burn, but they don't burn at a steady rate. For example, one fuse could take 59 minutes to burn the first inch and then burn the rest of the fuse in the last minute.
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