You have two ropes. Each of them burns for one hour. They burn unevenly in different parts though – it means that one half can burn for 20 minutes and other half for 40 minutes. In addition you have a box of matches.
You only need to light both ends of one rope and one end of the other. When the first burns out you light the second end of second rope. Half hour is burned away from that one already. The rest burns out in 15 minutes, burning from both ends.
You only need to light both ends of one rope and one end of the other. When the first burns out you light the second end of second rope. Half hour is burned away from that one already. The rest burns out in 15 minutes, burning from both ends.