there are two lengths of rope...
each one can burn in exactly one hour
they are not necessarily of the same length or width as eachother
they are also not of uniform width... (they may be thikcer in the middle than the other end).. so burning half rope is not necessarily 30 minutes
by burning the two ropes... how do you measure 45 minutes worth of time?
2006-12-15 07:19:25 · 5 answers · asked by laurentvanwinckel 2 in Science & Mathematics ➔ Mathematics
Light the end of one rope, and light *both* ends of the second rope.
That second rope, which is burning at double the rate will be consumed after 30 minutes. At that point, you have used up 30 minutes of the first rope, with 30 minutes remaining.
Now, use the same trick and light the other end of the remaining rope. Burning at twice the rate, it will be fully consumed in half the time (15 minutes), for a total elapsed time of 45 minutes.
2006-12-15 07:27:36 · answer #1 · answered by Puzzling 7 · 6⤊ 1⤋
Start them both burning at the same time, except on one of them you light both ends. This rope with both ends lit burns for 30 minutes. When it burns out, burn the other end of the 2nd rope. This 2nd rope will only last 15 minutes more. Tada, 45 minutes.
2006-12-15 15:38:50 · answer #2 · answered by slider 2 · 0⤊ 0⤋
You don't, I think. But if you can chop the ropes, you automatically increase their surface, no matter how long etc each initial piece is, and you can reduce the total burning time.
Or am I missing something?
2006-12-15 15:27:12 · answer #3 · answered by supersonic332003 7 · 0⤊ 1⤋
check you watch
2006-12-15 15:25:59 · answer #4 · answered by answerman 4 · 0⤊ 4⤋
With your watch...
2006-12-15 15:25:27 · answer #5 · answered by Jennifer T 1 · 0⤊ 4⤋