Two Fuses


You have two fuses, one which burns for exactly 1 hour and one 
which burns for exactly 2 hours. Neither fuse burns at a constant
rate so, for example, the last few inches of the first fuse could
take 5 minutes or 55 minutes to burn. 

You have as many matches as you want. With these fuses, your task
is to measure a time period of exactly 45 minutes. 

How do you do this?
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Answer:
Light the one hour fuse at both ends while simulataneously lighting
the 2 hour fuse at one end only. Since the first fuse will be burning
from both ends, it will be comsumed twice as fast and be gone in 
1/2 hour.  At that time 1.5 hours (90 minutes) will remain on the 
second fuse.  So, as soon as the first fuse burns out, light the 
second end of the 2 hour fuse.  Since it will now be comsumed twice
as fast, it will now burn up in exactly 45 minutes.