《小数乘法的简便运算》(用)

1、,小数乘法的简便计算,（复习课）,1、看谁算得快,1.258 =,2.54 =,10,10,0.50.2= 500.2= 5000.2=,0.1,10,100,2.50.4 =,1,0.2540 =,10,1.250.8=,1,1.2580=,100,2、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、看谁算得巧,(234)15,25734,10232,= 25473 = 10073 = 7300,= 23(415) = 2360 = 1380,= (100+

2、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：,b=b,乘法结合律：,(b) c= (bc),乘法分配律：,(+b) c=c+bc,4.21.69 2.50.770.4（ 6.13.6+3.93.6（ ）,填一填,1.69,4.2,2.5,0.4,0.77,6.1,3.9,3.6,1、,14.78 4.78,0.254.784,0.65201,1300.65 130.65,0.2544.78,0.65（2001）,0.652000.65,根据乘法交换律,乘法分配律,2、看谁用的准？,小数乘法简便计算应注意的问题

3、： 一审： 审清题目。 二看： 观察数字特征，选择合理的运算定律。 三算： 认真计算。 四查： 查运算顺序；查数字；查每一步的计算。,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)(8 1.25) = 110 = 10,760.8+0.27.6,0.8599+0.85,= 7.60.8+0.27.6 = 7.6(0.8+0.2) = 7

4、.61 = 7.6,= 0.8599+0.851 = 0.85(99+1) = 0.85100 =85,你能用几种方法进行简便计算？,0.254.4,应用拓展,挑战自我,7.61.01,（8+0.8） 1.25,9.28139.284+9.28,下面的算式，你能进行简便计算吗？,（1）1.25322.5 （2）3.20.6+60.28 （3）1.2528,用简便方法计算（说说我是怎样想的， 理由是什么,计算时应注意什么）。,(1)12.54.8(2)1.012.6 (3)3.89.9,1、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= 5