整數(shù)乘法運(yùn)算定律推廣到小數(shù)乘法課件

1、整數(shù)乘法運(yùn)算定律推廣到小數(shù)乘法,執(zhí)教 潘亮宇,1）2.3+7 6.8-6 9-1.9,口 算,9.3,0.8,7.1,2）3.8-0.3-0.7 2.6+1.1-2.6 2+80.5,2.8,1.1,6,結(jié)論：整數(shù)乘法的交換律、結(jié)合律和分配律， 對(duì)于小數(shù)乘法同樣適用,25954 448+648 10156 2532,25950.4 44.8+64.8 1010.56 253.2,觀察兩組算式有何不同,說(shuō)說(shuō)你是怎樣想的,說(shuō)說(shuō)你的計(jì)算想法,25495=10095=9500,48(4+6)=4810=480,(100+1) 56=5600+56=5656,25(48)=2548=1008=800,2

2、5954 448+648 10156 2532,說(shuō)出計(jì)算第一步,500.130.2 1.250.70.8 0.32.50.4,500.20.13,1.250.80.7,0.3（2.50.4,選擇（把正確的編號(hào)填在括號(hào)里,4282.5=28 (2.5 4)這題根據(jù)(,1)乘法分配律 (2)乘法交換律 (3)乘法結(jié)合律 (4)乘法交換律和結(jié)合律,4,1.250.70.8,選擇一組計(jì)算,1.250.80.7 =10.7 =0.7,7.8(100-1) =7.8100-7.81 =772.2,0.3(2.50.4) =0.31 =0.3,5.6(9.3+0.7) =5.610 =56,7.899,5.

3、69.3+5.60.7,0.32.50.4,0.65201 7.899,0.65,變一變,7.8,1,1,0.65（201-1） =0.65200 =130,7.8（99+1） =7.8100 =780,1.253.22.5,1.25（40.8）2.5 =1.250.8（42.5） =110 =10,試一試,不能直接運(yùn)用定律和性質(zhì)時(shí), 只有通過(guò)對(duì)某一個(gè)數(shù)進(jìn)行拆數(shù)后, 才能運(yùn)用定律和性質(zhì)使計(jì)算簡(jiǎn)便,8.881.25,8.881.25,8.881.25,8.881.25,(81.11) 1.25 =81.251.11 =101.11 =11.1,(8+0.8+0.08) 1.25 =81.25+0

4、.81.25+0.081.25 =10+1+0.1 =11.1,(8.888) (1.258) =1.1110 =11.1,計(jì)算2.82.08 +8.22.08 - 2.08 的簡(jiǎn)便方法( )是正確的。 (1) 2.8 (2.8 + 8.2-1) (2) 2.08 (2.8+ 8.2 + 1) (3) 2.8 (2.8 + 8.2) (4) 2.08 (2.8 +8.2-1,選擇（把正確的編號(hào)填在括號(hào)里,4,判 斷,(,15+15)(6.4+3.6,(,2.5（4-0.8）1.25=2.541.25-2.50.81.25-(,43100-1,4399,43(100-1,25 15) 4,254 +15 4,25 4) 15,15 6.4 +153.6,(,15(6.4+3.6,2.53.21.25=(2.54)(0.81.25,王叔叔買了梨和蘋(píng)果各45千克，梨每千克0.8元，蘋(píng)果每千克4.2元，一共花了多少錢,王阿姨家辦酒席，買25箱果粒純飲料，每箱8瓶，每瓶5.6元，共需要多少錢,解：45（4.2+0.8）=225（元） 答：一共花了225元,解：85.625=1120（元） 答：共需要1120元,1、 4.42.5 2、 12.5(0.8+0.8) 2.5 3、 4.621235.7,闖三關(guān)（簡(jiǎn)算,整數(shù)乘法的交換律、結(jié)合律