《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,14.78 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,（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 =0.7,4.21.69 2.50.770.4（ ） 6.13.6+3.93.6（ ）,填一填,1.69,4.2,2.5,0.4,0.77,6.1,3.9,3.6,3.64.5+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)(8 1.25) = 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