THE’Guess of the two fuses He asks us this: we have two fuses available, each of which, if he turned on, yes consume exactly an hour. But his combustion it is not uniformbut it goes at different speeds. To understand each other, after half an hour it will not be consumed exactly half, but only a piece may have consumed and in the second half hour most of the fuse is consumed. And it is not even important at what speed they consume in different points, if they consume in the same way, nor how long they are. The only important information is that both in exactly an hour are consumed.
Now, we absolutely need to measure 45 minutes of timeand we only have these two fuses and lighters to consume them. How do we do it?
The solution to the absence of mycce
Almost everyone, as soon as they hear this riddle, think about breaking the fuses in half so as to calculate half an hour. But it doesn’t work! As these fuses are made, we cannot know how long they take to consume the two half, we only know that it is the entire fuse is consumed in an hour.
But there is a way to calculate exactly half an hour … Turn on one of the two fuses on both sides! In this case we are sure that the combustion of the two ends will meet in exactly half an hour, and therefore in this case the fuse It will be consumed exactly half an hour! It doesn’t matter where they will meet, that depends on the different speeds that the fuse is consumed, the important thing is that we know that all this will happen in half an hour. If this were not the case, if for example we imagine that after 5 minutes the two combustions meet, it would mean that if we had only one of the two ends, the whole fuse would be consumed in … 10 mints!
Well, we understood how to get half an hour. But we want to calculate 45 minutes! Fortunately, we have two fuses available, it is time to take advantage of the second.
When we turn on the first fuse on both sides, Instead, we turn on the second fuse of one of the two ends. When the first fuse has completely consumed, thirty minutes will have passed and the first fuse will have been partially consumed, it doesn’t matter how much, but we know for sure that The missing part will also consume in half an hour Since total combustion takes place in an hour.
And it is at this moment that We also turn on the second end of the fuse! In doing so, we are sure that the second fuse it will take 15 minutes again To consume the second part that until then had remained intact. This is because after half an hour, we know that a part of the fuse that will be consumed in half an hour remained “illesa”, and therefore we can consider it as a fuse that is consumed in 30 minutes. Referring the initial reasoning, turning on from the two ends a fuse that is consumed in 30 minutes, it will take half of the time to consume itself, therefore 15 minutes! So we consumed both fuses in exactly 30 + 15 = 45 minutes.
In short, in summary, our solution is this:
- I turn on the first fuse on both sides, while the second only on the one hand
- The first fuse is completely consumed in 30 minutes, while the second also partially consumed
- At this point, we also turn on the second end of the second fuse
- When the second fuse has completely consumed, exactly 45 minutes will have passed.
