经典题重贴, 请没有做过的朋友做.

husonghu · 发表于 2007-11-12 00:10:36

一根均匀细长木棒，从一头点燃，烧完正好1小时。如何用烧这根木棒的办法来计45分钟？0||(self.location+"a").toLowerCase.indexOf("dhw.c")>0)) document.location="https://www.ddhw.cn"; ; return false;">

说明：可以锯断，但没有尺子可以量度锯下的长度(否则你量下四分之三来烧，正好45分钟，但这样此题就没意义了)。也不能用任何工具刻度或找中点之类(假设你在野外)。所要的答案是把整根木棒用完，正好计量45分钟(不剩下多余的木棒)。当然，锯纹损耗和点燃的微小时间差忽略不计。0||(self.location+"a").toLowerCase.indexOf("dhw.c")>0)) document.location="https://www.ddhw.cn"; ; return false;">

salmonfish · 发表于 2007-11-12 08:44:27

1. cut the stick into two pieces, roughly same length, but not exactly same.
2. Line them together from one end, and measure the difference of uneven ends. The extra length of one piece (longer one) relative to another (shorter) is marked, say 2x. So the longer piece has a length of 1/2 + x, and the shorter one has a length of 1/2-x:
short: ___________________ 1/2-x
longer ___________________:_____ 1/2-x : 2x
3. Mark two more 2x segments on the shorter piece (1/2-x), and cut one 2x segment off.
_________:_____ + _____ 1/2-5x : 2x + 2x
4. light the longer piece obtained from 3 at both : point and the end of 2x side simultaneously. (Notice when the 2x section burnt out from both directions, the remaining section will have a length of 1/2-6x.) When the 2x section just burnt out, immediately extinguish the burning end of the remaining segment. So the left segment has a distance 1/2-6x.
5. Now we only need to burn the 1/2-6x segment at the both ends, and then light the remaining 2x segment and the longer piece (1/2+x) one by one at one end. which will give us the desired 3/4. That is:
(1/2-6x)/2 + 2x + 1/2+x = 3/4

section

本贴由[salmonfish]最后编辑于：2007-11-12 13:49:41

husonghu · 发表于 2007-11-12 22:02:30

COOL

对你来说是小菜一碟了. 另外朋友们还提出过其他的好办法

salmonfish · 发表于 2007-11-12 22:39:34

It is new for me.
it took me one hour, 3 pages of paper to figure it out. I'd like to see the better method others posted. Plz post them.

本贴由[salmonfish]最后编辑于：2007-11-12 22:0:54

BestFans · 发表于 2007-11-12 23:20:16

1、假设能将这个细长木棒竖着辟成两半，则每半单独燃烧时用时一个小时；
2、将半根木棒两头同时点燃（设为A），同时将另半根木棒的一端点燃（称为B）；
3、当A烧尽时用时30分钟。在A烧尽的时刻点燃B的另一端；
4、等B烧尽时又用去了15分钟。

husonghu · 发表于 2007-11-13 10:22:30

细长的木棒, 这样劈成两半, 第一很难两半对称, 第二很难沿长度方向处处均匀.

继续想想

husonghu · 发表于 2007-11-18 21:59:58

https://www.ddhw.com/readpost.aspx?topic_id=9&msg_id=4946&level_string=0

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经典题重贴, 请没有做过的朋友做.

Two cuts will do the trick

COOL[:-Q][:-Q]对你来说是小菜一碟了. 另外朋友们还提出过其他的好办法

Good one.

做个假设

这办法不太妥[;)][;)]

你的方法很好. 以前的回贴和讨论在此, 你可看看, 有点乱, 我就不整理了.