Your job is to measure 45 minutes, if you have only two cords and matches to light the cords.
1. The two cords are twisted from various materials and so their different segments can burn at different rates.
2. Each cord burns from end to end in exactly one hour.
Describe your way of measuring the 45 minutes.
Start fire on both ends of one igniter cord and on one end of the second igniter cord. The very moment the first cord (where both ends burn) stops burning (that is after 30 minutes), start fire on the other end of the second cord (otherwise it would burn another 30 minutes). Thus the second igniter cord burns just 15 minutes from then. And that is all together 45 minutes.