- By The Anonymous BEACON Puzzler (who wishes to remain so).
Rope Burn
You have two ropes, cleverly designated by your Anonymous BEACON Puzzler as Rope #1 and Rope #2. The ropes are of different lengths and material but you know that each is long enough to burn for exactly one hour. Both ropes vary in thickness and content along their length such that individual sections will burn at completely different rates. For example, half of a rope may take more or less than half an hour to burn. You have no other timing devices, no ruler, and no way to cut rope. You do have a box of matches and your faithful Chihuahua dog Miss Barkalot.
How can you use the ropes to measure 45 minutes?
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Rope can be burning from more than one place.
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1 - Light both ends of Rope #1 and one end of Rope #2.
2 - When Rope #1 is completely consumed, 30 minutes has elapsed. Immediately light the unlit end of Rope #2.
3 - When Rope #2 has burned all the way, another 15 minutes will have elapsed.
The total elapsed time for both ropes to have been burned is 45 minutes.
Even though parts of a rope may be burning at different rates, when both ends are burning the remaining piece will be consumed twice as fast and thus in half the time. Rope #1 will be completely consumed after 30 minutes and at that time there will still be 30 minutes left on Rope #2. By lighting the other end of Rope #2 at that point it will be completely consumed in 15 more minutes.
Miss Barkalot is key to this puzzle since she will spend the entire 45 minutes hopping around barking at the rope, ensuring that you do not doze off at any point during the solution.
