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整数乘法运算律推广到小数,R,五年级上册,乘法交换律：,a,b,=,b,a,乘法结合律：,(,a,b,),c,=,a,(,b,c,),乘法分配律：,(,a,b,),c,=,a,c,b,c,乘法有哪些运算律？,一、复习导入,你会算吗？,运用了整数乘法的运算律，计算变简单了！,2534,4,1836+1864,25,4,34,100,34,3400,18,(36+64),18,100,1800,运用乘法交换律,运用乘法分配律,一、复习导入,整数的乘法运算律能不能推广到小数中呢,？,我觉得可以。,不一定能。,二、探究发现,0.7,1.2,1.2,0.7,（,2.4,3.6,）,0.5,0.8,（,0.5,0.4,）,你还能举出具有上面规律的算式吗？,观察下列每组的两个算式，它们有什么关系？,（,0.8,0.5,）,0.4,2.4,0.5,3.6,0.5,0.84,0.84,0.16,0.16,3,3,=,=,=,二、探究发现,0.7,1.2,1.2,0.7,（,2.4,3.6,）,0.5,0.8,（,0.5,0.4,）,观察下列每组的两个算式，它们有什么关系？,（,0.8,0.5,）,0.4,2.4,0.5,3.6,0.5,0.84,0.84,0.16,0.16,3,3,=,=,=,二、探究发现,能不能找到一个相反的例子？,0.7,1.2,1.2,0.7,（,2.4,3.6,）,0.5,0.8,（,0.5,0.4,）,观察下列每组的两个算式，它们有什么关系？,（,0.8,0.5,）,0.4,2.4,0.5,3.6,0.5,0.84,0.84,0.16,0.16,3,3,=,=,=,二、探究发现,从上面的算式中，你发现了什么规律呢,？,0.7,1.2,1.2,0.7,（,2.4,3.6,）,0.5,0.8,（,0.5,0.4,）,观察下列每组的两个算式，它们有什么关系？,（,0.8,0.5,）,0.4,2.4,0.5,3.6,0.5,0.84,0.84,0.16,0.16,3,3,=,=,=,二、探究发现,整数乘法的交换律、结合律和分配律，对于小数乘法也适用。,0.25,4.78,4,0.25,4,4.78,1,4.78,4.78,怎样使计算更为简便呢？,运用了哪个运算律？,乘法交换律。,【,课本,12,页例,7】,0.25,4,0.65202,=,0.65,（,200,2,）,=,=,130,1.3,131.3,= 0.65200,0.652,怎样使计算更为简便呢？,把202分成200+2，然后用乘法分配律计算比较简便。,【,课本,12,页例,7】,先,观察,算式的整体结构,。,在小数乘法中，要使计算简便我们要注意什么？,1,观察数据特点。,选择合适的运算律简便计算。,2,3,2.5,（,0.77,0.4,）,=,（,）,1.,根据运算律填空,。,4.2,1.69,7.2,8.4,2.8,8.4=,（,）,1.69,4.2,2.5,0.4,0.77,7.2,2.8,8.4,乘法交换律,乘法结合律,乘法,分配,律,【,课本,P12,做一做,】,三、巩固练习,2.,用简便方法计算下面各题,。,101,0.45,（,100,1,）,0.45,100,0.45,1,0.45,45,0.45,45.45,【,课本,P12,做一做,】,0.034,0.50.6,0.034,（,0.5,0.6,）,0.034,0.3,0.0102,4.75,99,4.75,（,99,1,）,4.75,100,4.75,475,你算对了吗？,2.73,99,2.73,（,100,-,1,）,2.73,100,-,2.73,1,273,-,2.73,270.27,2.,用简便方法计算下面各题,。,【,课本,P12,做一做,】,4.,用简便方法计算下面各题,。,【,课本,13,页练习三第,4,题,】,4.80.25,0.7898,0.78,（,100,2,）,0.78,100,0.78,2,78,1.56,76.44,1.2,4,0.25,1.2,(4,0.25,),1.2,1,1.2,0.52.33,8,1.5105,0.5,8,2.33,4,2.33,9.32,1.5,（,100,5,）,1.5,100,1.5,5,150,7.5,157.5,4.,用简便方法计算下面各题,。,【,课本,13,页练习三第,4,题,】,6.,小玲的爸爸、妈妈带着她和,2,名同学去公园游玩。公园成人票每张,5,元，儿童票每张,2.5,元，他们买门票一共需要多少钱？,【,课本,13,页练习三第,6,题,】,你知道了哪些数学信息？,25+32.5,10,+,7.5,17.5,（元）,答：买门票一共需要,17.5,元。,7.,纯净水每瓶,1.3,元，买,5,箱纯净水一共要花多少钱？,2451.3,120,1.3,156,（元）,答：一共需要花,156,元。,【,课本,14,页练习三第,7,题,】,先求出一共多少瓶水。,241.35,245,1.3,156,（元）,120,1.3,先求出一箱水多少钱。,乘法交换律：,a,b,b,a,乘法结合律：,(,a,b,),c,a,(,b,c,),乘法分配律：,(,a,b,),c,a,c,b,c,整数乘法的交换律、结合律和分配律，对于小数乘法也适用。,四、总结收获,
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