Critical Section


two fuse puzzle

Wednesday,  02/05/20  11:24 PM

Unrelated to three dog night :)

you are a wizard...The other day I asked: "Imagine that you're making a magic potion. You're a wizard with a long beard. But - the potion only works if you wait exactly 45 minutes before you stir it. If you stir it before or after the potion's totally ruined. You don't have a smartphone. You don't have a watch. You don't have any kind of time measuring device. What you have is two fuses of irregular consistency. The one thing you know for a fact is that it takes an hour for each of these fuses to burn from one end to the other. How do you use these to measure exactly 45 minutes?"

  • Ignore that you're a wizard with a long beard.
  • Take the first fuse, and light both ends.  At the same time light one end of the second fuse.
  • After exactly 30 minutes, the flames from the two ends of the first fuse will meet and the fuse will go out.
  • At that moment, light the other end of the second fuse.
  • After exactly 15 more minutes, the flames from the two ends of the second fuse will meet and the fuse will go out.
  • Poof!  Time to stir the potion.

Cheers!

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