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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,*,*,小数乘小数,回顾反思,自主练习,合作探索,情境导入,课后作业,1,今天我当家,小数乘法,QD,五年级上册,一、情境导入,你会计算这三道题吗？,0.15,0.09=,0.48,0.06=,1.4,1.25=,0.2 8 8,0.4 8,0.0 6,0.0 2 8 8,0.4 8,0.0 6,0.48,0.06=,？,0.288,你会计算,0.48,0.06,吗？,二、合作探索,积是,0.288,还是,0.0288,？为什么？,0.0288,？,继续,0,0,.,.,.,.,0.4 8,0.0 6,2 8 8,添,0,补位,0.0288,0.48,0.06=,？,积的小数位数不够怎么办？,二、合作探索,两位小数,两位小数,四位小数,你会计算,0.48,0.06,吗？,二、合作探索,小数乘法并不难，化成整数把积算，,数清因数小数位，再点积中小数点，,小数位数如不够，积前添0位补全。,0.15,0.09,0.0,1 3 5,0.1 5,0.0 9,0.0135,1.,你会计算,0.15,0.09,和,1.4,1.25,吗？,1.4,1.25,5 0 0,1.2 5,1.4,1.75,1 2 5,1,.,7 5,0,试一试,0.0 2 3,0.4,0.0 0 9 2,1.0 5,0.0 2,0.0 2 1 0,试一试,2.,用竖式计算。,计算小数乘法时，先按整数乘法的计算法则来计算，再看因数中一共有几位小数，就从积的右边起数出几位，点上小数点。小数末尾有,0,要去掉，小数前面位数不够用,0,补上。,想一想，怎样计算小数乘法？,试一试,二、合作探索,（选题源于,典中点,）,0.3 6,0.0 8,0.0 2 8 8,（）位小数（）位小数,(,),位小数，积的小数位,数不够，要在前面用,(,),补,足，再点上,(,),。,1.,填一填。,(1),(2)0.630.03,的积有,(,),位小数。,(3)0.0250.08,的结果是,(,),。,两,两,四,0,小数点,四,0.002,2,算一算。,(1),比比谁算得快。,二、合作探索,0.00408,5.76,4.08,5.76,4.08,0.576,二、合作探索,(2),直接写得数。,0.60.7,0.520.1,1.70.2,0.224,2.50.04,0.32.1,(3),用竖式计算。,0.650.13,4.020.38,0.06512,0.080.46,0.42,0.052,0.34,0.88,0.1,0.63,0.0845,1.5276,0.78,0.0368,二、合作探索,3,填一填。,(1),一个因数不变，另一个因数缩小到原来的,，积就,(,),，两个因数同时分别缩小到原来的,，积就,(,),。,(2),两个因数的积是,8.45,，如果两个因数同时扩大为原来的,10,倍，则积是,(,),。,(3),一个数,(0,除外,),乘一个比,1,大的数，积就,(,),这个数；乘一个比,1,小的数,(0,除外,),，积就,(,),这个数。,845,大于,小于,缩小到原来的,缩小到原来的,二、合作探索,4.,在,里填上,“,”“,”,或,“,”,。,180.35 0.35,3.921 3.92,1.6770.98 1.677,2.04 6.32.04,4.80.75 7.54.8,二、合作探索,5,根据第一栏的积写出后面每栏的积。,因数,27,27,2.7,0.27,0.27,因数,16,1.6,1.6,1.6,0.16,积,432,43.2,4.32,0.432,0.0432,1.,计算小高手。,0.0 9,0.8,0.0 7 2,0.4 7,0.2,0.0 9 4,0.4 3,0.1 6,0.0 6 8 8,三、自主练习,2.,先判断积的小数位数，再计算。,0.1 2 4,0.9,0.1 1 1 6,0.0 5 7,0.0 6,0.0 0 3 4 2,0.4 6,0.0 3,0.0 1 3 8,三、自主练习,四位,五位,四位,3.,0.6,米,0.85,米,0.72,米,0.85,0.6=0.51,（平方米）,三、自主练习,0.72,0.72=0.5184,（平方米）,0.51,平方米,0.5184,平方米,0.5184-0.51=,0.0084,（平方米）,答：,正方形,的面积大，大,0.0084,平方米。,哪个图形的面积大？大多少平方米？,4.,在 里填上,“,”,“,三、自主练习,5.,妈妈为喜欢读书的莉莉办了一张借,书证（如右图），这张借书证的面,积是多少平方分米？,1.2,分米,0.8,分米,=,0.96,（平方分米）,答：借书证的面积约是,0.96,平方分米。,三、自主练习,1.2,0.8,4,402,0.402,6.,连一连。,三、自主练习,40.2,4.02,0.0402,134,3,13.4,3,1.34,0.3,1.34,3,1.34,0.03,三、自主练习,易错辨析,（选题源于,典中点,）,6,下面的计算对吗？不对的请改正。,(1)0.420.03,0.126,0.4 2,0.0 3,0.1 2 6,(),改正：,0.420.03,0.0126,0.4 2,0.0 3,0.0 1 2 6,三、自主练习,(2)0.250.037,0.0925,0.2 5,0.0 3 7,1 7 5,7 5,0.0 9 2 5,(),改正：,0.250.037,0.00925,0.2 5,0.0 3 7,1 7 5,7 5,0.0 0 9 2 5,辨析：积的小数位数不够时，在,前面补,0,且要,补够,。,三、自主练习,7,判断。,(,对的画“”，错的画“,”),(1),一个因数比,1,小时，积一定小于另一个因数。,(,),(2),一个数的,1.5,倍一定比原数大。,(,),辨析：,一个不为,0,的数乘,小于,1,的小数，积一定,小于,这个数。一个不为,0,的数乘,大于,1,的小数，积一定,大于,这个数。,四、回顾反思,
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