Fuse puzzle help

August 3rd, 2013

The Puzzle: In front of you are several long fuses. You know they burn for exactly one hour after you light them at one end. The entire fuse does not necessarily burn at a constant speed. For example, it might take five minutes to burn through half the fuse and fifty-five minutes to burn the other half.
With your lighter and using these fuses, how can you measure exactly three-quarters of an hour of time?
my solution:
Fold a fuse in half, and fold another fuse in half. Light both sides of the first fuse and light one side of the other folded fuse simultaneously, when the second fuse finishes burning you will have exactly three-quarters of an hour.
Is this correct?

Answer #1
Not quite.
Light one fuse on one end, and another on both ends. When the fuse with both ends lit finishes burning exactly 30 minutes have passed. Light the other end of the second fuse at this time and it will finish burning in 15 minutes. There’s your 45 minutes.
Answer #2
Wouldn’t my way work also? I saw that solution online aswell.
Answer #3
Nope. With your way the first fuse will burn out in 30 minutes and the second fuse will take an hour.
Answer #4
The first one would burn out in 15 minutes, it’s folded and both sides are lit. The second would be 30 minutes as it’s folded and only one side is lit.
Answer #5
Ok I understand what you’re trying to do. You still have a fault in your logic.
If you light both folded fuses at the same time then the total time would be 30 minutes, which is the burn time for the one with the single end lit. If you lit the second as soon as the first went out you would get your 45 minutes. This method only works if the burn rate is consistent. This could possibly be achieved with the given fuses if they are twisted tightly enough to ensure that they act as a single thick fuse. A loosely folded fuse may still burn inconsistently giving an unknown time.
Answer #6
Like Spudster says..
Light one fuse at both ends and, at the same time, light the second fuse at one end. When the first fuse has completely burned, you know that a half hour has elapsed, and, more relevantly, that the second fuse has a half hour left to go. At this time, light the second fuse from the other end. This will cause it to burn out in 15 more minutes. At that point, exactly 45 minutes will have elapsed.
http://www.rinkworks.com/brainfood/s/discrete44.shtml
Answer #7
Spudster replied: Ok I understand what you're trying to do. You still have a fault in your logic.
If you light both folded fuses at the same time then the total time would be 30 minutes, which is the burn time for the one with the single end lit. If you lit the second as soon as the first went out you would get your 45 minutes. This method only works if the burn rate is consistent. This could possibly be achieved with the given fuses if they are twisted tightly enough to ensure that they act as a single thick fuse. A loosely folded fuse may still burn inconsistently giving an unknown time.

Thanks for explaining it but i don’t think you’re on the same lines as me of what i’m saying.
If you fold a fuse in half and light it at one end then the total time would be 30 minutes no? As if you light a non-folded fuse on both ends it would be 30 minutes right? So then if you light ONE of the folded fuses at both ends (15 minutes as it would burn 4x as fast, due it to be in half and lit at both ends), and one of the folded fuses at one end (or one unfolded fuse at both ends).
Answer #8
What you’re saying has merit, however you’re still not adding the burn times together to achieve 45 minutes.
Lighting BOTH folded fuses at the same time would cause the one lit at both ends to burn out in 15 minutes, and the other to burn out 15 minutes later to give you a time of 30 minutes. That’s simple arithmetic.
Answer #9
Spudster replied: What you're saying has merit, however you're still not adding the burn times together to achieve 45 minutes.
Lighting BOTH folded fuses at the same time would cause the one lit at both ends to burn out in 15 minutes, and the other to burn out 15 minutes later to give you a time of 30 minutes. That's simple arithmetic.

So would lighting the folded one at both ends first (15 mins) then lighting a folded one at one end or a non-folded one at both ends (30mins), right?
Answer #10
Lemonpwns replied: So would lighting the folded one at both ends first (15 mins) then lighting a folded one at one end or a non-folded one at both ends (30mins), right?
That’s right. Either one will work.
Answer #11
Spudster replied: Lemonpwns replied: So would lighting the folded one at both ends first (15 mins) then lighting a folded one at one end or a non-folded one at both ends (30mins), right?
That's right. Either one will work.

Alright thank you with sticking with me!

 

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