《小数乘法的简便运算》.ppt

,小数乘法的简便运算,1看谁算得快,0.32100,0.40.5,1.258,2.54,0.245,0.60.1,=32,=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,教学目标,理解整数乘法运算定律对小数乘法同样适用，并会用这些定律进行一些小数的简便运算。,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=()-(),0.08,10,0.01,0.02,0.2,3、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,25734,(234)15,10232,=25473=10073=7300,=23(415)=2360=1380,=(100+2)32=10032+232=3200+64=3264,比一比看谁算得巧,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。,问题,14.784.78,0.254.784,0.65201,1300.65130.65,0.2544.78,0.65（2001）,0.652000.65,根据乘法交换律,乘法分配律,（1）0.1256.80.8,（2）2.80.25,=0.1250.86.8=0.16.8=0.68,=40.70.25=40.250.7=10.7=0.7,4.21.692.50.770.4（）6.13.6+3.93.6（）,填一填,1.69,4.2,2.5,0.4,0.77,6.1,3.9,3.6,3.64.5+3.65.5可以运用（）进行简算。,A、乘法交换律B、乘法结合律C、乘法分配律,C,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=10,0.258.54,1.288.6+0.728.6,=0.2548.5=18.5=8.5,=(1.28+0.72)8.6=28.6=17.2,0.8599+0.85,760.08+0.27.6,1.288.6+0.828.6-0.86,=0.8599+0.851=0.85(99+1)=0.85100=85,=7.60.8+0.27.6=7.6(0.8+0.2)=7.61=7.6,=1.288.6+0.828.6-8.60.1=8.6（1.28+0.82-0.1）=8.62=17.2,完全达标,课堂小结,作业课本1617页练习,