小学数学五年级上册《小数乘法的简便运算》PPT课件

-,1,小数乘法的简便运算,-,2,看谁算得快,0.32100,240.24,150.15,0.40.5,1.258,2.54,0.245,0.60.1,=32,=24.24,=14.85,=0.2,=10,=10,=1.2,=0.06,0.50.2=500.2=5000.2=,0.1,10,100,2.50.4,=1,0.2540,=10,1.250.8,=1,1.2580,=100,-,3,2、在括号里填上适当的数。,(1)0.32=4()(2)1.02=1+(),(3)0.99=1-()(4)9.8=()-(),0.08,10,0.01,0.02,0.2,-,4,看谁算得巧,(234)15,25734,10232,=25473=10073=7300,=23(415)=2360=1380,=(100+2)32=10032+232=3200+64=3264,-,5,3、思考：乘法有哪些运算定律？怎样用字母式子表示？,乘法交换律：,ab=ba,乘法结合律：,(ab)c=a(bc),乘法分配律：,(a+b)c=ac+bc,-,6,观察下面每组的两个算式，它们有什么关系？,=,=,=,整数乘法的交换律、结合律和分配律，对于小数乘法同样适用。,-,7,14.784.78,0.254.784,0.65201,1300.65130.65,0.2544.78,0.65（2001）,0.652000.65,例8,根据乘法交换律,乘法分配律,-,8,(1)0.0340.50.8(2)0.1256.80.8(3)2.80.25,-,9,4.21.692.50.770.4（）6.13.6+3.93.6（）,填一填,1.69,4.2,2.5,0.4,0.77,6.1,3.9,3.6,-,10,A、乘法交换律B、乘法结合律C、乘法分配律,3.64.5+3.65.5可以运用（）进行简算。,C,-,11,7.60.8+0.27.6,0.2536,0.8599,0.25321.25,=7.6(0.8+0.2)=7.61=7.6,=0.2549=19=9,=0.85(100-1)=0.85100-0.851=85-0.85=84.15,=0.25481.25=(0.254)(81.25)=110=10,-,12,760.08+0.27.6,0.8599+0.85,=7.60.8+0.27.6=7.6(0.8+0.2)=7.61=7.6,=0.8599+0.851=0.85(99+1)=0.85100=85,-,13,0.258.54,1.288.6+0.728.6,0.25(8.5+8.5+8.5+8.5),1.288.6+1.444.3,1.288.6+0.828.6-0.86,=0.2548.5=18.5=8.5,=(1.28+0.72)8.6=28.6=17.2,=(1.28+0.82-0.1)8.6=28.6=17.2,=1.288.6+0.828.6-0.18.6,=0.25(8.54),=1.288.6+0.7224.3,=1.288.6+0.728.6,-,14,回顾一下，通过本节课的学习，你有哪些新的收获？,小数计算应注意的问题：一审：审清题目。二看：观察数字特征，选择合理的运算律。三算：认真计算。四查：查运算顺序；查数字；查每一步的计算。,-,1