Probably: You have two identical ropes. If you light a rope on fire, it will finish burning in exactly one hour. The burn rate is inconsistent - there is no re

Probably: You have two identical ropes. If you light a rope on fire, it will finish burning in exactly one hour. The burn rate is inconsistent - there is no relationship between how much of the rope has burned, and how much time has passed, until the rope has fully burned away. How can you use the two ropes to measure 15 minutes? Given that it's printed in cracking the coding interview, Google has almost certainly banned this problem.