You have two wooden sticks. They burn completely in 1 hour. You have a match box to light the sticks. The sticks are of uneven density so they don't burn evenly, but completely burn in an hour. How can you use them to measure half an hour? How can you use them to measure 45 minutes?

To measure half an hour: Light a stick from both sides. It will completely burn off in half an hour.

To measure 45 minutes: Light a stick from both sides and light the other stick from 1 side. After the first stick completely burns that is half an hour later. Light the half burning stick from the other side as well and you get 45 minutes.