小数乘法的简便运算,执教：赵彩霞 单位：渔户寨乡中心小学,1、口算（直接写出得数）。,(1)0.50.2= (2)500.2= (3) 5000.2=,(4)2.44= (5)2.50.4= (6)0.2540=,(7)0.1258= (8)12.58= (9)1.2580=,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=( )-( ),0.1,1,100,9.6,10,10,1,100,100,0.08,10,0.01,0.02,0.2,引入阶段,(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)=ab+ac,整数乘法的这些运算定律是否适用于小 数乘法呢 -（ ）,？,例1： 李阿姨计划买1袋面粉（42元/袋）、2千克牛肉（46.4元/千克）、2千克鱼（23.6元/千克），她带200元钱,够吗？,整数乘法的这些运算定律是否适用于小 数乘法呢 -（ ）,适 用,探究阶段 猜一猜，算一算，议一议,=,=,=,0.84,0.84,0.16,0.16,30,30,0.61.1 1.10.6,=,（0.40.5）0.2 0.4（0.50.2）,=,（1.25 + 2.5）0.8 1.250.8+2.50.8,=,乘法交换律： ab = ba,乘法结合律：（ab）c=a（bc）,乘法分配律：（ab）c=ac + bc,交流验证,14.78 4.78,0.254.784,0.65201,1300.65 130.65,0.2544.78,0.65（2001）,0.652000.651,试一试,运用阶段:,应用乘法运算定律填空。 （1）7.80.81.25 =() （2)（8+10）12.5 =+ （3）1.74.2+1.75.8 =(+),7.8,0.8,1.25,8,10,12.5,12.5,5.8,1.7,4.2,7.60.8+0.27.6,0.2536,0.8599,760.08+0.27.6,0.25321.25,0.8599+0.85,= 7.6(0.8+0.2) = 7.61 = 7.6,= 0.2549 = 19 = 9,= 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)(8 1.25) = 110 = 10,= 0.8599+0.851 = 0.85(99+1) = 0.85100 =85,11.116666+777833.33,培优阶段,用多种方法思考？,这节课学的怎样？,自我评价:,谢 谢,