Question: You have two heterogeneous none breakable sticks,(heterogeneous means that the sticks are not identical and do not burn at a constant rate) such that each stick needs 1 hour to be totally burned if it is lit from only one end. How can these two sticks be used to time 45 minutes?
Answer: You burn the first stick from its two ends at once (you get 30 minutes from the first stick); simultaneously you burn the second one from one end . When the first one has been totally burned(the first 30 minutes have passed), you burn the second stick from its other end (you get 15 minutes from the second stick). So you get 45 minutes