You have 2 lengths of fuse. Each will burn exactly one hour. But the fuses are not necessarily identical and do not burn at a constant rate. There are fast burning sections and slower burning sections. How do you measure exactly 30 minutes using only the fuses and one lighter?
And what about 45 minutes?
2007-10-21 09:09:07 · 4 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
For 30 minutes, you take both ends of one fuse and light the sides simultaneously. When the two burnt ends meet (i.e. the fuse bruns up), it will be exactly 30 minutes, as each end burned half the fuse's time away.
For 45 minutes, you take both ends of one fuse and one end of the other and light them all simultanously again. Here, when the first fuse burns itself out (the ends meet), you light the other end of the second fuse. The first fuse measured 30 minutes and the two sides burning on the second fuse measure another 15, for a total of 45.
2007-10-21 09:23:17 · answer #1 · answered by Expat Mike 7 · 2⤊ 0⤋
1. Ignite one fuse from 2 ends simultaneously. Total time to burn is 30 minutes.
2. Ignite one fuse like in 1 and at the same time ignite the second fuse from one end. After 30 minutes measured by first fuse ignite the second end of the second fuse. This fuse will burn out in 45 minutes.
2007-10-24 07:15:31 · answer #2 · answered by Alexey V 5 · 2⤊ 0⤋
Look at the clock?
2007-10-21 09:15:14 · answer #3 · answered by Kyle G 3 · 1⤊ 3⤋
do it
2007-10-21 09:17:07 · answer #4 · answered by ExDy 1 · 0⤊ 3⤋