小數(shù)乘法,十位,百位,千位,萬位,十分位,百分位,千分位,萬分位,萬,千,百,十,十分之一,0.1,百分之一,0.01,千分之一,0.001,萬分之一,0.0001,1.5里面有( )個0.1 1.5里面有( )個0.5,15,3,小數(shù)乘法的計算法則:先按整數(shù)乘法算出積,看因數(shù)里共有幾位小數(shù),就從積的右邊起數(shù)出幾位小數(shù),點上小數(shù)點.,試一試,0.514 2.3(積精確到十分位 ),0.514 12.3,試一試,3.04 7.02(積保留1位小數(shù)),3.06 7.02=30.6 ( ),智力挑戰(zhàn)題,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,智力挑戰(zhàn)題,1.41.2 1.4,2.270.2 2.27 3 0.38 0.3 0.95,1、一塊玻璃長3.1米,寬2米, 如果每平方米玻璃的價格的3元,買這塊玻璃需要多少錢?,智力挑戰(zhàn)題,18.6元,100塊夠.,2、學校圖書館的面積是120平方米,用邊長1.1米的正方形地磚鋪地,100塊夠嗎?,智力挑戰(zhàn)題,3噸.,3、1公頃森林每天殺菌40千克,2.5公頃森林6月份殺菌多少噸?,智力挑戰(zhàn)題,30分鐘不能到,4、王先生從家到公司騎摩托車,每分鐘行10千米,要用15分鐘,如果他改用騎自行車,每分鐘行4千米,35分鐘到嗎?,智力挑戰(zhàn)題,看誰算得快,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、在括號里填上適當?shù)臄?shù)。,(1)0.32=4( ) (2)1.02=1+( ),(3)0.99=1-( ) (4)9.8=( )-( ),0.08,10,0.01,0.02,0.2,看誰算得巧,(234)15,25734,10232,= 25473 = 10073 = 7300,= 23(415) = 2360 = 1380,= (100+2)32 = 10032+232 = 3200+64 = 3264,3、思考：乘法有哪些運算定律？ 怎樣用字母式子表示？,乘法交換律：,ab=ba,乘法結(jié)合律：,(ab) c=a (bc),乘法分配律：,(a+b) c=ac+bc,觀察下面每組的兩個算式，它們有什么關(guān)系？,=,=,=,整數(shù)乘法的交換律、結(jié)合律和分配律，對于小數(shù)乘法同樣適用。,14.78 4.78,0.254.784,0.65201,1300.65 130.65,0.2544.78,0.65（2001）,0.652000.65,例8,根據(jù)乘法交換律,乘法分配律,(1)0.0340.50.8 (2)0.1256.80.8 (3)2.80.25,A、乘法交換律 B、乘法結(jié)合律 C、乘法分配律,3.64.5+3.65.5可以運用（ ）進行簡算。,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,回顧一下，通過本節(jié)課的學習，你有哪些新的收獲？,小數(shù)計算應(yīng)注意的問題： 一審：審清題目。 二看：觀察數(shù)字特征，選擇合理的運算律。 三算：認真