1、,第3課時(shí) 整數(shù)加法運(yùn)算定律推廣到小數(shù),四年級(jí)下冊(cè),教者：何 亮,一、復(fù)習(xí)導(dǎo)入,在里填上適當(dāng)?shù)姆?hào)。,32+55+32 (47+26)+7447+(26+74),3.2+0.50.5+3.2 (4.7+2.6)+7.44.7+(2.6+7.4),你有什么發(fā)現(xiàn)？,=,=,加法交換律,加法結(jié)合律,兩邊的結(jié)果相等嗎？,3.2+0.50.5+3.2 (4.7+2.6)+7.44.7+(2.6+7.4),今天我們就來(lái)學(xué)習(xí)小數(shù)加減法的簡(jiǎn)便計(jì)算。,整數(shù)加法的交換律、結(jié)合律對(duì)小數(shù)加法同樣適用。,應(yīng)用運(yùn)算定律，可以使一些小數(shù)計(jì)算更簡(jiǎn)便。,=,=,二、新課講授,計(jì)算 0.6+7.91+3.4+0.09,0.6+7

2、.91+3.4+0.09 =8.51+3.4+0.09 =11.91+0.09 =12,你準(zhǔn)備怎樣計(jì)算？,有更簡(jiǎn)單的方法嗎？,0.6+7.91+3.4+0.09,+,4,+,8,(0.6+3.4)+(7.91+0.09) =4+8 =12,在計(jì)算時(shí)應(yīng)用了什么運(yùn)算定律？,應(yīng)用了加法交換律和加法結(jié)合律。,0.6+7.91+3.4+0.09 =8.51+3.4+0.09 =11.91+0.09 =12,0.6+7.91+3.4+0.09 (0.6+3.4)+(7.91+0.09) =4+8 =12,兩種方法有什么相同點(diǎn)和不同點(diǎn)。,結(jié)果相同,從左往右的順序依次計(jì)算的,運(yùn)用了加法交換律和結(jié)合律,3.3,

3、1.38,1.75,0.25,上面各式分別運(yùn)用了什么運(yùn)算定律？,加法交換律,加法結(jié)合律,你會(huì)算嗎？,2. 計(jì)算下面各題，怎樣簡(jiǎn)便就怎樣計(jì)算。,1.88+2.3+3.7 =1.88+(2.3+3.7) =1.88+6 =7.88,13.7+0.98+0.02+4.3 =(13.7+4.3)+(0.98+0.02) =18+1 =19,3.計(jì)算出四（1）班450米跑接力賽的總時(shí)間。,你能快速算出結(jié)果嗎？,+,=17,+,=17,+,=34,4.口算。,0.384+0.37+2.63= 5.28+3.43+0.72= 1.29+3.6+0.71+6.4=,3.384,12,9.43,在小數(shù)四則混合運(yùn)算中要仔細(xì)觀察每個(gè)數(shù)的特征，注意數(shù)與數(shù)之間的關(guān)系及每個(gè)數(shù)前面的運(yùn)算符號(hào)，恰當(dāng)