数学五年级小数乘法.ppt

小数乘法,十位,百位,千位,万位,十分位,百分位,千分位,万分位,万,千,百,十,十分之一,0.1,百分之一,0.01,千分之一,0.001,万分之一,0.0001,1.5里面有( )个0.1 1.5里面有( )个0.5,15,3,小数乘法的计算法则:先按整数乘法算出积,看因数里共有几位小数,就从积的右边起数出几位小数,点上小数点.,试一试,0.514 2.3(积精确到十分位 ),0.514 12.3,试一试,3.04 7.02(积保留1位小数),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 ( ),0.0818,80,1.40.99 1.4,智力挑战题,1.41.2 1.4,2.270.2 2.27 3 0.38 0.3 0.95,1、一块玻璃长3.1米,宽2米, 如果每平方米玻璃的价格的3元,买这块玻璃需要多少钱?,智力挑战题,18.6元,100块够.,2、学校图书馆的面积是120平方米,用边长1.1米的正方形地砖铺地,100块够吗?,智力挑战题,3吨.,3、1公顷森林每天杀菌40千克,2.5公顷森林6月份杀菌多少吨?,智力挑战题,30分钟不能到,4、王先生从家到公司骑摩托车,每分钟行10千米,要用15分钟,如果他改用骑自行车,每分钟行4千米,35分钟到吗?,智力挑战题,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= 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,看谁算得巧,(234)15,25734,10232,= 25473 = 10073 = 7300,= 23(415) = 2360 = 1380,= (100+2)32 = 10032+232 = 3200+64 = 3264,3、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,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。,14.78 4.78,0.254.784,0.65201,1300.65 130.65,0.2544.78,0.65（2001）,0.652000.65,例8,根据乘法交换律,乘法分配律,(1)0.0340.50.8 (2)0.1256.80.8 (3)2.80.25,A、乘法交换律 B、乘法结合律 C、乘法分配律,3.64.5+3.65.5可以运用（ ）进行简算。,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 = 10,760.08+0.27.6,0.8599+0.85,= 7.60.8+0.27.6 = 7.6(0.8+0.2) = 7.61 = 7.6,= 0.8599+0.851 = 0.85(99+1) = 0.85100 =85,0.258.54,1.288.6+0.728.6,0.25(8.5+8.5+8.5+8.5),1.288.6+1.444.3,1.288.6+0.828.6-0.86,= 0.2548.5 = 18.5 =8.5,= (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,回顾一下，通过本节课的学习，你有哪些新的收获？,小数计算应注意的问题： 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