Light the first rope at both ends and the second at one end, at the same moment. The first burns out in exactly 30 minutes, however unevenly, because the two flames meet. Light the other end of the second then, and it burns out 15 minutes later.
You have two ropes. Each takes exactly an hour to burn from end to end, but they burn unevenly, so half a rope won’t necessarily take half an hour. With a lighter and nothing else, how do you measure exactly 45 minutes?
Give me a hintThe hint
There is more than one place to light a rope.
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Light one rope at both ends and the other at one
Source: Traditional, an interview puzzle by the early 2000s, origin unknown