小數(shù)乘法同步奧數(shù)

小數(shù)乘法,小數(shù)乘法的簡(jiǎn)便計(jì)算,一、復(fù)習(xí)舊知,直接寫出得數(shù)。,（1）0.50.2（2）500.2（3）5000.2,（4）2.54（5）2.50.4（6）0.2540,（7）0.1258（8）12.58（9）1.2580,0.1,1,100,10,10,10,1,100,100,一、復(fù)習(xí)舊知,乘法交換律：,abba,乘法結(jié)合律：,(ab)ca(bc),乘法分配律：,(ab)cacbc,乘法有哪些運(yùn)算定律？怎樣用字母式子表示？,二、探索新知,0.71.2,1.20.7,（0.80.5）0.4,（2.43.6）0.5,0.8（0.50.4）,2.40.53.60.5,0.84,0.16,3,0.84,0.16,3,小數(shù)四則混合運(yùn)算的順序跟整數(shù)是一樣的。,比一比，看誰(shuí)算得又對(duì)又快！,觀察每組的兩個(gè)算式，它們有什么關(guān)系？,二、探索新知,0.71.2,1.20.7,（0.80.5）0.4,0.8（0.50.4),（2.43.6）0.5,2.40.53.60.5,從上面的算式中，你發(fā)現(xiàn)了什么規(guī)律？,整數(shù)乘法的交換律、結(jié)合律和分配律，對(duì)于小數(shù)乘法也適用。,應(yīng)用乘法的運(yùn)算定律，可以使一些計(jì)算簡(jiǎn)便。,二、探索新知,0.254.784,運(yùn)用運(yùn)算定律計(jì)算,0.2544.78,1,4.78,4.78,怎樣使計(jì)算更為簡(jiǎn)便呢？,二、探索新知,0.1250.250.564,運(yùn)用運(yùn)算定律計(jì)算,0.1250.250.5842,1,（0.1258）（0.254）（0.52）,怎樣使計(jì)算更為簡(jiǎn)便呢？,111,練習(xí)一：,1、1.3112.582（1.312）（12.58）2.621002622、1.25320.251.25840.25（1.258）（40.25）10110,練習(xí)二：,3、1.25881.25（808）（1.2580）（1.258）10010110,0.652020.65（2002）0.652000.6521301.3131.3,例題：,乘法分配律,三、知識(shí)應(yīng)用,（二）用簡(jiǎn)便方法計(jì)算下面各題,1010.45,4.75994.75,（1001）0.45,1000.4510.45,450.45,45.45,（991）4.75,1004.75,475,你算對(duì)了嗎？,例題：,例：1.251.081.25（10.08）（1.251）（1.250.08）1.250.11.35,練習(xí)一：,1、2.510.42.5（100.4）（2.510）（2.50.4）25126,練習(xí)二：,2、16.080.125（160.08）0.125（280.125）（0.080.125）20.012.01,例題：,例：用簡(jiǎn)便方法計(jì)算下面各題。1010.45(1001)0.451000.4510.45450.4545.45,練習(xí)一：,1、7.59.97.5（100.1）（7.510）（7.50.1）750.7574.25,練習(xí)二：,2、3.80.993.8（10.01）（3.81）（3.80.01）3.80.0383.762,練習(xí)三：,3、0.125920.125(1008)(0.125100)(0.1258)12.5111.5,3、4.6994.64.6994.614.6（991）4.6100460,3（2）：7.51017.57.51017.517.5（1011）7.5100750,練習(xí)二：,2、9973.273.29973.273.2173.2（991）73.21007320,例題：,例：399.6919980.8（399.65）（95）19980.819981.819980.81998（1.80.8）199811998藍(lán)色的兩個(gè)數(shù)有什么關(guān)系？倍數(shù)關(guān)系！他倆是五倍的關(guān)系！,練習(xí)一：,1、400.6720030.4400.67400.650.4400.67400.62400.6（72）400.652003,練習(xí)二：,2、2397.29568.22397.223948.22397.223932.8239（7.232.8）239409560,練習(xí)三：,3、2751216502333007.527512275623275127.52751227513827590275（1213890）2756016500,例題：,例：1.99920031.99820041.99920031.998（20031）1.99920031.99820031.99812003（1.9991.998）1.99820030.0011.9982.0031.9980.005,練習(xí)一：,1、19.94201019.93201119.94201019.93（20101）19.94201019.93201019.9312010（19.9419.93）19.9320100.0119.9320.119.930.17,練習(xí)二：,2、1.232.451.222.461.232.451.22（2.450.01）1.232.451.222.451.220.012.45（1.231.22）0.01222.450.010.01220.02450.01220.0123,練習(xí)三：,3、3.620133.520143.620133.5（20131）3.620133.520133.512013（3.63.5）3.520130.13.5201.33.5197.8,練習(xí)卷,1、0.80.0412.525（0.812.5）（0.0425）10110,2、16.080.125（160.08）0.125160.1250.080.125280.1250.080.12520.012.01,3、9973.273.273.2（991）73.21007320,4、0.254.730.1253200.254.730.125408（0.2540）（0.1258）4.731014.7347.3,5、4.72.83.69.4（4.72）（2.82）3.69.49.41.43.69.49.4（1.43.6）9.4547,6、3.754.862.50.483.75104.81062.50.4837.50.4862.50.480.48（37.562.5）0.4810048,7、13.817513.717613.817513.7（1751）13.817513.717513.71175（13.813.7）13.71750.113.717.513.73.8,8、3.62323613.23603.6232361013.2103603.62323.61323603.6（232132）3603.610036