Est. 1998 — 27 years of woodworking knowledge
Friday Puzzler -- Fuses
Alex Y
You are given two pieces of fuse cord, which are each guaranteed to burn for exactly 1 hour. However, they do not burn at a constant rate--e.g., half of the length of a given cord may be burned in only 20 minutes, while the other half takes 40 minutes to burn.
How can you measure exactly 45 minutes using these two cords (and a lighter, of course)?
Re: Friday Puzzler -- Fuses
Ed in Leaside
... something about burning the candle at both ends. 3-2
Correct!
Re: Friday Puzzler -- Fuses
Larry Barrett
So with Ed's obscure hint, and Alex's confirmation that it is correct, I think I see how this works. I surmise that you can precisely determine 30 minutes and 45 minutes, but not 15 minutes (or any other time within the hour). Is this correct?
Re: Friday Puzzler -- Fuses
Alex Y
I don't see how you could determine any other time within the hour, but I don't see right away any way to prove that you can't.
In any case, it is clear you properly interpreted Ed's hint.
Re: Friday Puzzler -- Fuses
Alex Y
Well, thinking about this a little more, I guess you could measure 15 minutes, but only starting 30 (or more if you can extinguish a burning fuse then relight it) minutes from now ;-)