Puzzle

thesubstitute said:
Another simple one:

You have two fuse wires and you know that the fuse wires are known to burn at various speeds along its own length. However you do know for certain that each fuse will burn out in an hour exact.

With no other equipment besides a lighter, how do you measure 45 minutes?
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I got this question in an interview once.
I didn't quite get all the way there in the pressure of the interview, but apparently did better than the other candidates who just sat there in silence and I ended up getting the job!
 
thesubstitute said:
Folding wouldn't actually work too well, since each of the 1/4 segments would still be burning at various speeds, some will burn out faster and others slower, which means they won't burn out at the right time.

You are thinking along the right lines though.
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yer, was thinking along the lines of twisting them together to even out the burn between the strands. Although the point about a larger quantity of fuse burning quicker than a single section...
 
Assuming you only need to measure 45 minutes and can be present the whole time (rather than needing to light and leave) then the following should work...

light both ends of one fuse, and at the same time light one end of the second fuse. The fuse with both ends lit will be completely burnt in 30 minutes, at this point light the other end of the second fuse which will then take a further 15 minutes to burn out completely.
 
Bill Door said:
Assuming you only need to measure 45 minutes and can be present the whole time (rather than needing to light and leave) then the following should work...

light both ends of one fuse, and at the same time light one end of the second fuse. The fuse with both ends lit will be completely burnt in 30 minutes, at this point light the other end of the second fuse which will then take a further 15 minutes to burn out completely.
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that wouldn't work. The 1st fuse would burn in 30min but the 2nd fuse would have ROUGHLY 30 min left due the varying speed at which it burns

EDIT: actually i think you might be right there!
 
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mame said:
that wouldn't work. The 1st fuse would burn in 30min but the 2nd fuse would have ROUGHLY 30 min left due the varying speed at which it burns
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he lit it at the same time as the first fuse ;)

you agree that the first fuse has burnt for 30mins, so the other fuse has been burning for exactly the same time (30mins).

so it must still have 30mins burning time left :)
 
must be something like, tear the 1 fuse into 4 parts then light all 4 parts at the same time as lighting the 2nd intact fuse. 45 min would be from when the last of the 4 parts was burnt out untill the 2nd intact fuse was burnt out ?


edit: hmm i don't think that would work because out of the 4 parts there could be a 20min part !
 
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