There is a certain kind of rope which takes exactly one hour to burn from end to end. The rope is not uniform,

Question

There is a certain kind of rope which takes exactly one hour to burn from end to end. The rope is not uniform, not symmetric - thicknesses throughout its length vary randomly. No two such ropes will be identical.
You have two such ropes. How will you measure 45 minutes?

Answer 1

Start burning the both ends of the first rope and one end of the second rope at the same time. The moment the first rope burns out, start burning the other end of the second rope. It will be 45 min when everything burned out.