You have two ropes, each of which takes one hour to burn completely. Both of these ropes are non-homogeneous in thickness, meaning that some parts of the ropes are chunkier than other parts of the rope. Using these non-homogeneous ropes and a lighter, time 45 minutes.
Some clarification on what is meant by non-homogeneous:
- For instance, maybe a particular section of rope that is 1/8 of the total length is really chunky, and takes 50 minutes to burn off. Then it would take 10 minutes to burn off the remaining 7/8, since we know that the whole rope takes an hour to burn off.
- That's just an example; we don't know any such ratios beforehand. The point is, if you look at one of your ropes and cut it into pieces, you have no clue how long any individual piece will take to burn off.