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 Rope Puzzle:

There are two lengths of rope.
Each one can burn in exactly one hour.
They are not necessarily of the same length or width as each other.
They also are not of uniform width (may be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour.

By burning the ropes, how do you measure exactly 45 minutes worth of time?
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Scroll down for  Answer
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Ah! Do try work it out first.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

OK, so you give up
 
 
 
 
 
 
 
 
 
 
 
 
 
 

If you light both ends of one rope, it will burn in exactly a 1/2 hour. Thus,
burn one rope from both ends and the other rope from only one end. Once the
 one rope (which is burning from both ends) finally burns out (and you
know a 1/2 hour has elapsed), you also know that the other rope (which is burning from
only one end) has exactly 1/2 hour left to burn. Since you only want 45 minutes, light
 the second end of the rope. This remaining piece will burn in 15 minutes.
Thus, totaling 45 minutes.