分数简便方法.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,R,五年级下册,第,2,课时 分数加减简便运算,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,望谟县新屯街道红岩小学,教师：王昌华,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,请你用简便方法计算下面各题，并说出简算的依据。,53,36,47 1.5,3.8,6.2,=53,47,36,=1.5,（,3.8,6.2,）,加法交换律：,a,+,b,=,b,+,a,加法结合律：（,a,+,b,）,+,c,=,a,+,（,b,+,c,）,复习导入,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,加法交换律：,a,+,b,=,b,+,a,加法结合律：（,a,+,b,）,+,c,=,a,+,（,b,+,c,）,请你说一说式中的字母可以表示什么数？,可以表示,整数、小数、分数,。,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,探究新知,下面每组算式的左右两边有什么样的关系？,2,5,+,3,7,3,7,+,2,5,(,+)+,1,4,3,4,2,3,+(,+),1,4,3,4,2,3,猜想一下 里应该填什么符号？,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,观察这些算式，你发现了什么？,2,5,+,3,7,3,7,+,2,5,(,+)+,1,4,3,4,2,3,+(,+),1,4,3,4,2,3,第一个算式左右两边的数都一样，就是交换了位置，很像整数中的加法交换律。,a,+,b,=,b,+,a,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,观察这些算式，你发现了什么？,2,5,+,3,7,3,7,+,2,5,(,+)+,1,4,3,4,2,3,+(,+),1,4,3,4,2,3,第二个算式只是改变了加的顺序，很像加法结合律。,（,a+b,）,+c=a+,（,b+c,）,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,2,5,+,3,7,3,7,+,2,5,(,+)+,1,4,3,4,2,3,+(,+),1,4,3,4,2,3,整数加法的,交换律,和,结合律,对分数加法同样适用。利用运算定律可以使一些分数计算变得简便。,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,请你再举几个分数加法的例子来验证一下，看看我们得出的结论是否正确。,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,=+,（,+,）,1,12,7,12,5,6,=+,8,12,5,6,+,+,1,12,7,12,5,6,=,9,6,=,1,2,1,+,2,7,1,3,2,3,1,5,=+,+,2,7,1,3,2,3,1,5,=1+,2,7,1,5,=1+,+,10,35,7,35,=1,17,35,4,6,算算看。,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,用简便方法计算下面各题。,+,1,3,2,5,3,5,=+,1,3,2,5,3,5,=1+,1,3,=1,1,3,+,1,3,1,4,2,3,1,4,=+1,1,2,(),(),=+,1,3,1,4,1,4,2,3,=1,1,2,+,1,8,9,7,5,7,3,8,(),(),=+,1,8,9,7,5,7,3,8,=2 +,1,2,=2,1,2,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,巩固提升,1.,计算 时，可采用加法的（）使计算简便。,交换律,结合律,交换律和结合律,+,5,16,7,9,11,16,2,9,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,(),(),+,1,10,3,8,9,10,5,8,+,1,10,3,8,9,10,5,8,=,+,1,12,1,7,11,12,=,+,1,7,(),(),(),(),(),+=,5,16,3,7,3,16,4,7,(),(),(),(),+,(),(),(),(),2.,在 里填上合适的运算符号，在括号里填上适当的数。,+,+,1,12,11,12,5,16,3,7,3,16,4,7,+,+,+,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,1,2,1,3,-,=,1,1,2,-,=,1,12,1,3,1,4,-,=,1,20,1,4,1,5,-,=,1,6,1,2,用你的发现计算下面这道题。,+,1,2,1,6,1,12,1,20,3.,你能发现什么？,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,1,n,1,n,+1,-,=,1,n,（,n,+1,）,（,n,0,）,归纳：,+,1,2,1,6,1,12,1,20,1,2,1,3,-,+,1,1,2,-,=,1,3,1,4,-,+,1,4,1,5,-,+,1,1,5,-,=,4,5,=,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,课堂小结,2,5,+,3,7,3,7,+,2,5,(,+)+,1,4,3,4,2,3,+(,+),1,4,3,4,2,3,整数加法的交换律和结合律对分数加法同样适用。,分数加减简便运算,课后作业,1.,课本,P100,，第,5,、,7,题；,2.,完成练习册本课时的习题。,