A rope burns non-uniformly and takes 1 hour to burn from end to end. How do you measure 45 minutes?

A rope burns non-uniformly and takes 1 hour to burn from end to end. How do you measure 45 minutes?

Approach: Light both ends of one rope, and one end of another simultaneously.

Light rope A at both ends and rope B at one end simultaneously. When A burns out (30 min), light other end of B. B will burn out in additional 15 min, total 45 min.

Follow-up: How to measure 15 minutes?

Key concepts: burn rate, symmetric burning, time calculation.