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bonanova · Daedalian Member

This is an old one with a twist. You have a fuse which burns at an uneven rate, but it's symmetrical about its midpoint. Starting from either end it burns completely in one hour. What is the shortest time interval it can measure?
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Courk · Daedalian Member

Do you have other tools available? I mean, you can do 1 second if you wanted: mark the midpoint, burn the fuse from end A for 1 second, extinguish it, measure the distance from the midpoint, and cut off the amount that burned from end B, and you now have a 1 second fuse.

bonanova · Daedalian Member

Other tools = scissors, matches, but no stopwatch.
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Nsof · Daedalian Member

i get 7.5 minutes by
1) cutting in half due to symmetry we are left with two 30 minutes.
2) light one of the halves in both sides until the two burning ends meet. cut the remaining half at the same distance from the end (using the symmetry). we get two 15 minute fuses left.
3) light one of the 15m fuses on both side and the second on just one end. Turn the second fuse off when the first completely burns. we are left with a 7.5 minutes fuse.
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Thok* · Guest

NSOF, your 7.5 minute fuse can be turned into a 3.25 minute fuse by lighting it on both ends.

referee · June 21st, 2004 Member

You mean 3.75.
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Courk · Daedalian Member

alphatango · Daedalian Member

I think Thok's point was that once you have the 7.5 minute fuse, you could light both ends of it.
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groza528 · No Place Like Home

Nsof, the fuse burns at an uneven rate, an therefore does not exhibit symmetry. Edit: Stupid me, I didn't read the original post very well. Sorry Revenge most foul!

I now agree with 3.75
bonanova: I assume "zero" is not the answer you were looking for? Revenge most foul!

Also, are we to assume that we only have one fuse?

bonanova · Daedalian Member

Right on all counts.
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