小数乘法简便计算练习课.ppt

小数乘法的简便计算,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,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,看谁算得巧,(234)15,25734,10232,=25473=10073=7300,=23(415)=2360=1380,=(100+2)32=10032+232=3200+64=3264,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,2.50.734,说一说,怎样计算比较好?,乘法交换律,=2.540.73,=100.73,=7.3,0.9612.50.8,说一说,怎样计算比较好?,乘法结合律,=0.96（12.50.8）,=0.9610,=9.6,0.2536,试一试,怎样计算比较好?,1.250.516,7.60.8+0.27.6,说一说,怎样计算比较好?,乘法分配律,=7.6（0.8+0.2）,=7.61,=7.6,（2.40.16）0.5,说一说,怎样计算比较好?,乘法分配律,=2.40.50.160.5,=1.20.08,=1.12,1.257.8（）,在括号里填上合适的数，使得计算简便。,8.61.28+0.72（）,8,8.6,0.8599,0.8599+0.85,比一比，有什么不同？,（7.04+2.96）1.24.250.99+0.01,比一比，能简算吗？,28.610128.6,0.8（4.31.25）,0.8615.70.8614.7,3.12+3.1299,27.69.8+0.227.6,0.2528,0.8599,760.08+0.27.6,0.25321.25,0.8599+0.85,=7.6(0.8+0.2)=7.61=7.6,=0.2547=17=7,=0.85(100-1)=0.85100-0.851=85-0.85=84.15,=7.60.8+0.27.6=7.6(0.8+0.2)=7.61=7.6,=0.25481.25=(0.254)(81.25)=110=10,=0.8599+0.851=0.85(99+1)=0.85100=85,0.25(8.5+8.5+8.5+8.5),2.41.02-0.048,1.288.6+1.444.3,1.288.6+0.828.6-0.86,=0.2548.5=18.5=8.5,=2.41.02-2.40.02=2.4(1.02-0.02)=2.41=2.4,=(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+0.728.6,3.067.02=30.6(),智力挑战题,0.702,1.41.02=0.14(),10.2,2.278.18=227()78=0.7(),0.0818,80,3.61.9+0.3681,7.62.4+6.57.6+7.6+0.76,智力挑战题,回顾一下，通过本节课的学习，你有哪些新的收获？,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