Everyone loves online riddles and thought puzzles, right? They can be fun and engaging, and they help exercise a part of your mind that doesn’t usually get stretched. Some of them are a bit difficult, but they all have solutions that are relatively simple once you hear them. One of the more difficult recent internet puzzles is the riddle of the two burning ropes. The set-up is quite simple. First, you are given two ropes and a lighter. You are told that each rope will burn in exactly 60 minutes if lit from a single end, but they don’t burn at a continuous rate. In other words, when half the rope is burnt, that doesn’t mean that it took 30 minutes to do so. With only the two ropes and a lighter, how could you measure either 45 or 50 minutes?
It may sound convoluted, but the solution is fairly straightforward. If burning one of the ropes from only one end takes 60 minutes, then burning it from both ends would take 30 minutes. The trick to measuring 45 minutes is to light both ends of one rope and a single end of the second rope. Once the rope with both ends burning has been burnt up, there will have been 30 elapsed minutes. The first rope will still be burning, and since it has burned for 30 minutes, the remainder of its burning time is 30 minutes. Now you simply need to light the second end of the remaining rope on fire, and it will burn twice as fast for the remaining 30 minutes, cutting down the time to 15 minutes. The total elapsed time from lighting the first rope is then 45 minutes.
To measure 50 minutes, you take the first method and expand upon it. Burning a rope from both ends cuts the time in half, but adding a third flame cuts the time into thirds, or 20 minutes. So, burn one of the ropes from both ends to reach 30 minutes, then light the second rope at one end and in the middle of the rope. Continuing lighting the center of the remainder of the rope so there are always two flames, and the total burning time for both ropes will be 50 minutes.
