How do we measure forty-five minutes using two identical wires, each of which takes an hour to burn. We have matchsticks with us. The wires burn non-uniformly. So, for example, the two halves of a wire might burn in 10 minute and 50 minutes respectively.
Heard from Sridhar Rajagopalan in 1998.
Light three out of four ends. When two ends meet, light the fourth!