1、5 小數(shù)乘法和除法 第16課時(shí) 整理與練習(xí),課時(shí)目標(biāo),1.回顧和整理本單元的內(nèi)容和方法，掌握小數(shù)乘、除法的計(jì)算方法和用計(jì)算器計(jì)算小數(shù)乘、除法。 2.能求積、商的近似值，能聯(lián)系實(shí)際合理運(yùn)用求近似值的方法，求出問(wèn)題結(jié)果的近似值。 3.通過(guò)解決練習(xí)中的問(wèn)題，體會(huì)成功探索規(guī)律的喜悅，感受數(shù)學(xué)的魅力，激發(fā)學(xué)習(xí)數(shù)學(xué)的興趣和積極性。,一、回顧引入,小組討論： 1.小數(shù)乘、除法的計(jì)算與整數(shù)乘、除法有什么聯(lián)系？ 2.計(jì)算小數(shù)乘法時(shí)，怎樣確定積的小數(shù)位數(shù)？ 3.怎樣把除數(shù)是小數(shù)的除法轉(zhuǎn)化成除數(shù)是整數(shù)的除法？,二、練習(xí)應(yīng)用,1.直接寫(xiě)出的數(shù)。,3.42,6.8,40.5,2,0.639,0.07,3.50.7,5,

2、0.70.8,0.56,0.250.05,5,二、練習(xí)應(yīng)用,2.算一算，比一比。,8.67,60.2,8.60.7,6.02,0.860.7,0.602,11.736,32.5,11.73.6,0.325,11.70.36,3.25,二、練習(xí)應(yīng)用,3.用豎式計(jì)算，并用計(jì)算器驗(yàn)算。,1.33.8,4.94,2.90.82,2.378,0.0720.15,0.0108,2.0424,0.085,0.7560.18,4.2,0.2560.032,8,二、練習(xí)應(yīng)用,4.計(jì)算下面各題，得數(shù)保留兩位小數(shù)。,0.172.45,0.42,2.60.54,1.40,7.313,0.56,7.832.8,2.80

3、,二、練習(xí)應(yīng)用,5.人的嗅覺(jué)細(xì)胞大約有0.048億個(gè)，狗的嗅覺(jué)細(xì)胞大約是人的45倍。狗的嗅覺(jué)細(xì)胞大約有多少億個(gè)？（得數(shù)保留一位小數(shù)）,0.04845,2.2（億個(gè)）,答：狗的嗅覺(jué)細(xì)胞大約有2.2億個(gè)。,二、練習(xí)應(yīng)用,（1）一種奶油蛋糕做1個(gè)要用7.5克奶油。50克奶油最多可以做多少個(gè)這種蛋糕？,507.5,6（個(gè)）,答： 50克奶油最多可以做6個(gè)這種蛋糕。,6.,（2）幼兒園買(mǎi)50個(gè)奶油蛋糕，每8個(gè)裝一盒，至少要用多少個(gè)包裝盒？,508,7（個(gè)）,答：至少要用7個(gè)包裝盒。,二、練習(xí)應(yīng)用,7.小明家七月份用水12.4噸，八月份用水13.6噸，九月份用水11.7噸。他家這三個(gè)月平均每月用水多少噸？

4、（得數(shù)保留整數(shù)）,答：他家這三個(gè)月平均每月用水13噸。,（12.413.611.7）3,37.73,13（噸）,二、練習(xí)應(yīng)用,8.先算一算，再比較每組題的得數(shù)，你有什么發(fā)現(xiàn)？,4.80.1,48,4.810,48,2.60.5,1.3,2.62,1.3,1.50.25,6,1.54,6,5.40.1,0.54,3.60.5,7.2,80.25,2,5.410,0.54,3.62,7.2,84,2,二、練習(xí)應(yīng)用,9.不計(jì)算，在里填“”或“”。,0.10.1,0.10.1,0.30.15,0.30.15,99.90.1,0.9990.1,3.22,3.22,二、練習(xí)應(yīng)用,10.計(jì)算下面各題，注意使

5、用簡(jiǎn)便算法。,4（9.35.7）3.6,0.67990.67,43.63.6,3.65,0.67（991）,0.67100,67,18,二、練習(xí)應(yīng)用,4.252.51011.7,6.81.256.88,1.71011.7,1.7（1011）,6.81.2586.8,6.8106.8,74.8,170,三、鞏固擴(kuò)展,11.用計(jì)算器算出下面每種食品1千克各是多少元。,20元,63.75元,42.5元,26.8元,三、鞏固擴(kuò)展,12.李曉芳用彩紙制作了一條花邊，一共排列了8朵花。每朵花的寬是4.5厘米，每相鄰兩朵花之間的距離是1.2厘米。你能算出這條花邊一共長(zhǎng)多少厘米嗎？,4.581.27,368.4,44.4（厘米）,答：這條花邊一共長(zhǎng)44.4厘米。,三、鞏固擴(kuò)展,13.先用計(jì)算器計(jì)算每組前三題，發(fā)現(xiàn)規(guī)律后直接寫(xiě)出后兩題的得數(shù)。,0.40.9,0.440.99,0.4440.999,0.44440.9999,0.444440.99999,0.36,0.4356,0.443556,0.44435556,0.4444355556,0.60.9,0.660.99,0.6660.999,0.66660.9999,0.666660.99999,0.