小数乘法简便计算练习课.ppt

1、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 = 1003

2、2+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,2.5 0.73 4,说一说,怎样计算比较好?,乘法交换律,=2.5 4 0.73,=10 0.73,=7.3,0.96 12.5 0.8,说一说,怎样计算比较好?,乘法结合律,=0.96 （12.5 0.8 ）,=0.96 10,=9.6,0.25 36,试一试,怎样计算比较好?,1.25 0.5 16,7.6 0.8 +0.2 7.6,说一说,怎样计算比较好?,乘法分配律,=7.6 （ 0.8

3、 +0.2 ）,=7.6 1,=7.6,（2.40.16） 0.5,说一说,怎样计算比较好?,乘法 分配律,=2.4 0.5 0.160.5,=1.2 0.08,=1.12,1.25 7.8（ ）,在括号里填上合适的数，使得计算简便。,8.61.28+ 0.72 （ ）,8,8.6,0.85 99,0.85 99 + 0.85,比一比，有什么不同？,（7.04+2.96）1.2 4.250.99+0.01,比一比，能简算吗？,28.6 101 28.6,0.8 （4.3 1.25 ）,0.86 15.70.86 14.7,3.12+3.12 99,27.69.8+0.227.6,0.2528,

4、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)(8 1.25) = 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

5、,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+0.728.6,3.06 7.02=30.6 ( ),智力挑战题,0. 702,1.4 1.02=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