How can you use these to measure 45 seconds?

Solution

Take two fuses. Light the first at *both ends*and light the second at just one end. As soon as the first burns out, 30 seconds will have passed. At this point, light the second at the remaining end. When this second fuse has burned out, forty-five seconds will have elapsed!

**Details:**The two ends that were lit will meet at exactly half of the burning time. If this were not true, the fuse could not burn for exactly one minute when lit at only one end. The point at which they meet might not be the middle though.

"The two ends that were lit will meet at exactly half of the burning time. If this were not true, the fuse could not burn for exactly one minute when lit at only one end."

ReplyDeleteUntrue.

No, it's a logical consequence. The burning time of each end must be summed. If they'd meet at e.g. 10 seconds then the whole fuse would take 20 seconds to burn. So the only way it would burn for the stated minute, is if the ends meet after 30 seconds exactly. (Still doesn't have to be the middle of the fuse.)

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