You have two pieces of delay fuse. One burns for 1 hour and the other burns for 30 minutes. Without a watch, clock, or timepiece at all... can you beyond any shadow of a doubt tell me when 45 minutes has elapsed using only a lighter or a match and the two delay fuses?
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3 Answers
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Answer
Fold each delay fuse and put them end to end and light one end. Once they've burned away, 45 minutes will have expired.
Reasoning
If the hour fuse and the 30 minute fuse are folded in half they will burn twice as fast because both halves are burning at the same time, thus giving a 30 minute timer and a 15 minute timer respectively.
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$\begingroup$ @DanChill took me a second to think of it haha. $\endgroup$– dcfyjMay 26, 2016 at 18:30
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Light both fuses from one end. When the 30 minute fuse is burnt out, 30 minutes has elapsed.
The 60 minute fuse is now a 30 minute fuse. Light it from the second end as well so it will burn twice as fast. When this has burnt out, and additional 15 minutes has elapsed and your 45 minutes is up.
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$\begingroup$ !> yes. or fold the 30 minute fuse in half and light the coupled end and when that goes out, light the 60 minute fuse at both ends. when the 60 minute fuse burns out, 45 minutes has elapsed. $\endgroup$ May 26, 2016 at 18:29
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Light both ends of the $60$ minute fuse, once this is finished ($30$ minutes) light both ends of the $30$ minute fuse ($15$ minutes).
