推荐回答(1个)
托尔斯泰喜欢的算术题
列夫 托尔斯泰是俄国伟大的文学家,曾创作了《战争与和平》、《安娜 卡列尼娜》、《复活》等世界文学名著.在文学工作之余,托尔斯泰对数学也很感兴趣,他还曾写过一本算术课本.在物理学家辛格尔的回忆录里,曾提到托尔斯泰很喜欢一道这样的算术题:
一组割草人要把两片草地的草割掉.大的一片草地比小的一片大一倍.上半天大家在大片地上工作,午后分成两组,一半人继续在大片地上割草,到傍晚收工时恰好割完;另一关人到小片地上割草,到傍晚还剩一小块.这一小块草地改日由一个人去割,恰好需要一天的工夫.问这组割草人的人数是多少?
提起”割草”这个问题,还有一段小故事呢.辛格尔的父亲和舅父,早年曾求学于莫斯科大学.其中有一位很有才华,但不幸早逝的同学,名叫彼得洛夫.彼得洛夫对当时学校铁教育方法有很大意见,认为学校只培养学生用死套公式的办法来解数学题,束缚了年轻的大学生们才能的发展.虽然他们往往能够找到既新颖又简洁的解题方法,但好像非采用死板的公式不可.于是彼得洛夫便自编了一些数学题,与同学们一起研究.”割草问题”便是其中一题.这个题目是经过辛格尔的父亲和舅父介绍,托尔斯才知道的.
托尔斯泰对这类外表看来非常复杂,可是往往有简易方法来解决的题目很感兴趣.事隔多年,当辛格尔会见托尔斯泰时,他已是一位白发苍苍的老人了,但对割草问题仍记忆犹新,称赞不已.他觉得特别有趣的是,这个题目如果利用图形来解,哪怕是画一幅最简单的草图,也更清楚简明得多.托尔斯泰画一张草图(如图1),他解释说:
因为大的一片草地需全组割草人割半天以后,还需一半割草人再割半天,那么很显然,一半割草人半天时间可割这块地的 .因此小片地上留下的没割的一块是大片地的 ,这样,1个割草人每天能割大片草地的 .而当天割草一共割了大片地的 倍,所以割草人共8人.
图解法,是一种非常简洁明了的解法.这个题目若用一般算术方法来解,则需要一定的技巧.但用代数中列方程的的并不困难.下面几种方程解法.
解法一:设割草人共 人.全体割草人干一天再加1个割草人干1天才割完两片草地,则1人割完需 +1天.割完两片草地的 需 天.另一方面,割小片草地 人干了 天,还需1人干1天,则1人需单独干需 天.从而
解得:
解法二:设割草人共 人,则一人割完两片地需 +1天.其中大片草地需 天.实际上全体裁割草人在大片地上割了半天,一人将用 天,一半人又在大片地割半天.一人将用 天.故可列方程:
解得:
解法三:一人割大片地需 天,割小片地用 天,大片地为小片地的2倍,所用天数亦是2倍.故意可弄方程:
解得:
解法四:设割草人共 人,每人每天割草面积为y.
大片地上 人割了 天, 人又割了 天,所以大片草地面积为 ,即 .1个人又割了1天,所以小片草地面积为 ,因为大片地是小片地面积的2倍,所以
解得: .
思考:从上面的故事体现的方程思想,你能用列方程的方法解决你所关心的某些问题。
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