第4课时约分（2）

状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,R,五年级下册,第,4,课时 约分（,2,）,复习旧知,把下面的分数约分。,16,36,24,32,30,45,16,（）,36,（）,16,36,=,=,（）,（）,4,9,4,4,24,32,=,24,（）,32,（）,=,（）,（）,3,4,8,8,30,（）,45,（）,30,45,=,=,（）,（）,2,3,15,15,这节课我们来继续探究约分。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,自主探究,先判断下列分数哪些是最简分数，把不是最简分数的数进行约分。,25,60,17,8,60,40,21,28,36,48,54,81,怎样判断一个分数是不是最简分数？,分子和分母只有公因数,1,的分数是最简分数。,1,我们要怎样进行分数的约分？,约分有两种方法：一种是用分子和分母共有的因数依次去除，一种是直接用分子和分母的最大公因数去除。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,25,60,17,8,60,40,21,28,36,48,54,81,25,60,=,255,605,=,5,12,21,28,=,217,287,=,3,4,54,81,=,5427,8127,=,2,3,60,40,=,6020,4020,=,3,2,36,48,=,3612,4812,=,3,4,2,甲数是,15,，乙数是,20,。,（,1,）甲数是乙数的几分之几？,你是怎么做的？,直接用甲数除以乙数就可以了。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1520=,3,4,（,2,）乙数是甲数的几分之几？,2015=,4,3,甲数是,15,，乙数是,20,。,（,1,）甲数是乙数的几分之几？,你会做了吗？试一试。,2,甲数是,15,，乙数是,20,。,2,（,3,）甲数是甲乙两数和的几分之几,?,这又该怎么做呢？,先求出甲乙两数的和，再按之前的方法求解。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,甲数是,15,，乙数是,20,。,2,（,3,）甲数是甲乙两数和的几分之几,?,15,（,15+20,）,=,3,7,15,35,在实际应用中我们要注意些什么？,要注意检查，能约分的一定要约分。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,约分的方法,小,结,方法一：,方法二：,直接用分子和分母的最大公因数去除。,用分子和分母共有的质因数依次去除。,01,02,约分的应用,小,结,求甲数是乙数的几分之几时用甲,乙计算，商用分数表示。,能约分的要约分。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1.,火眼金睛。（把正确答案的序号填在括号里）,A.1B.2C.3D.4,（,1,）,32,和,6,的公因数有（）个。,A.3B.4C.5D.6,（,2,）如果,a,、,b,的最大公因数是,18,，那么,a,和,b,的公因数有（）个。,B,D,随堂演练,2.,对号入座。,8,32,9,27,18,54,13,39,16,64,7,28,11,44,16,48,1,3,1,4,9,27,18,54,13,39,16,48,8,32,11,44,16,64,7,28,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,12,16,和,9,12,4,12,和,5,20,4,14,和,9,21,70,35,和,90,40,3,4,3,4,1,3,1,4,=,2,7,3,7,2,9,4,3.,先约分，再比较各组分数的大小。,4.,（,1,）以分米作单位，用分数分别表示长方形的长和宽。,4,5,分米,长：,3,5,分米,宽：,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,4.,（,2,）长是宽的几分之几？宽是长的几分之几？,4,3,长是宽的：,86=,3,4,宽是长的：,68=,4.,（,3,）涂出长方形面积的 ，你可以怎样涂？,可以用对角线将长方形平均分成两份，涂其中一份；也可以用对称轴将长方形平均分成两份，涂其中一份。,3,4,课堂小结,约分,方法,逐次约分法,一次约分法,求一个数是另一个数的几分之几用除法,甲,乙,=,甲,乙,（注意约分）,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1.,完成,P66,页，第,6,、,7,题；,2.,完成练习册本课时的习题。,课后作业,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,声 明,本文件仅用于个人学习、研究或欣赏，以及其他非商业性或非盈利性用途，但同时应遵守著作权法及其他相关法律的规定，不得侵犯本司及相关权利人的合法权利。,除此以外，将本文件任何内容用于其他用途时，应获得授权，如发现未经授权用于商业或盈利用途将追加侵权者的法律责任。,武汉天成贵龙文化传播有限公司,湖北山河律师事务所,