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1、期中复习,2015北师大版四年级下册,小数乘法、加减法竖式计算,一、计算类,小数加减法列竖式计算方法,要使相同数位对齐（也就是小数点对齐），从低位开始加减，最后在得数里对齐横线上的小数点的地方点上小数点。,小数竖式乘法计算,基本的过程：,抄写横式；,列竖式（准确对位）；,按整数乘法法则计算；,点上小数点；,检查，在横式写得数。,小数乘法的计算法则：,先按照整数乘法的法则算出积，再看两个乘数中一共有几位小数，就从积的右边起数出几位小数，点上小数点。,0.25 4.8 =,抄横式，写竖式，准确对位。,0.25 4.8 =,2 0 0,按照整数乘法法则计算，先算258，得200。,后算254，得10
2、0。,0.25 4.8 =,把两次求得的数加起来。这个得数就是“积”。,1 2 0 0,0.25 4.8 =,1 2 0 0,两位小数,一位小数,三位小数,0. 2 5, 4.8,2 0 0,1 0 0,1 2 0 0,从积的右边起数出三位小数，并点上小数点。,0.25 4.8 =,0.25 4.8 =,把小数末尾的“0”去掉。,1.2,检查、写得数。,思考： 在小数乘法竖式计算时我们应该要注意些什么?（格式、书写、过程和检查。）,竖式计算 12.3+4.12 23.5-2.8 20-3.65 3.84-2.3 5.1-1.23 2.8+4.65 4.8-2.8 1.03+12.5 3.1+2
3、.22 26.2-13.1 35.28-19.59 12.3+1.02,3.5103 0.7025 3.154 12.40.7 2.311.2 6.90.3 2.36.2 0.580.09 0.297,6.73 0.660.04 3.74.6,6.50.4= 561.33= 3.022.5= 2.61.8= 0.87= 3.516= 12.54= 1.82.3= 0.370.04= 1.0625= 78. 6= 9.60.39= 270.43= 1.745= 1.21.04= 0.374= 861.2= 2.40.15= 212.4= 4.328=,0.825= 2.583= 5.80.6=
4、3.60.4= 2.63.7= 1.560.18= 1.035.03= 0.2082= 1.111.1= 0.361.3= 2.56.5= 0.32.6= 0.9845= 3.22.5= 5.22.9= 0.688.1= 8.63.25= 0.3250.14= 3.25.06= 5.241.2= 18.2534=,9.354.2= 15.079.8= 7.020.56=,4.020.11 0.783.1 0.8422.5 33.6480 12.43.5 4033.5 1.431.7 8.022.8 1.363.7 0.250.08 2.80.65 1.83.4 6884 854416 6751
5、5,289918 10179 243264 12.43.5 16828 15624 4.020.11 0.783.1 0.8422.5 33.6480 4033.5 1.431.7 8.022.8,1.111.1 0.361.3 2.56.5 0.32.6 0.9845 3.22.5 5.22.9 0.688.1 8.63.25 0.3250.14 3.25.06 5.241.2 18.2534 9.354.2 15.079.8 7.020.56,小数加、减、乘法混合计算,在整数乘法中,我们学习了哪几种运算定律?,乘法交换律 ab=b a 乘法结合律 (ab)c=a(bc) 乘法分配律 (ab
6、) c=aCbc,(整数乘法的运算定律同样适用于小数),32.8 4 +17.2 4,4,4,=(32.8+17.2) 4 =50 4 =200,0.65201,=0.65 (200+1) =0.65 200+0.65 1 =130+0.65 =130.65,16.75-0.42-4.58,=16.75-(0.42+4.58) =16.75-5 =11.75,0.25 17 40 (10+0.1) 8.3 0.125 8.8 5.6+3.49+4.4+6.51,=0.25 40 17 =10 17 =170,=10 8.3+0.1 8.3 =83+0.83 =83.83,=0.25 4 2.2
7、 =10 2.2 =22,=(5.6+4.4) +(6.51+3.49) =10 +10 =20,.0.254.784,=4.78(0.254) =4.781 =4.78,2.5763+5737,=57(63+37) =5700,4.28.6 101 28.6,=28.6 (101 1),=28.6 100,=2860,0.8(4.31.25),= 0.81.25 4.3,= 1 4.3,= 4.3,(4.23 6.17) 0.8,3.254.8,8.2.855.2+2.855.82.85,9.3.69（1.695.8）,递等式计算 3.572881.43 15.694.885.12 3.81
8、.4-2.35 6.35-（2.43+3.35） 48.8-8.82.5 52.8920 4.82.35.22.3 (8+0.8) 1.25,48-1.80.25 3.80.254 74.875.2 5-（4.19-2.83）,4.28+0.53-3.37 1.54+2.08+3.62 2.5x13 + 0.9 2.6+ 1.4 X 3 0.25X3.7X 0.4 0.89X4.8 + 0.89X 5.2 1.83+3.79+0.17 10 0.34 0.66 2.5X 0.6 1.8X 0.5 4.15+3.24+9.85+6.76 3.2X4.6+3.2X5.4 12.8+2.04X9.5
9、,5.122.544.88 12.517.80.8 9.92.5 9.45.810.65.8 0.1250.320.25 9.6+9.699 2.87.6+1.42.8 +2.8 6.310.1 0.253.212.5 9.5101 3.791.6+6.391.6 12.50.42.58 4.27.8+2.24.2,3.723.56.283.5 36.83.96.1 2 5.48(9.40.52) 146.5(2346.5) 4.87.8780.52 3.6102 324.90.9 18.769.918.76 4.84.80.5 (1.250.125)8 4.8101 56.59.956.5
10、7.0910.80.87.09,4.025.40.98 5.171.83.2 13.75(3.756.48) 3.687.562.68 7.852.340.854.66 35.61.815.67.2 3.822.90.189.1 9.64.83.6 7.140.532.47 5.272.860.661.63 13.354.682.65 47.87.45+8.8,13.354.682.65 47.87.45+8.8 0.398+0.36+3.64 15.75+3.590.59+14.25 42.5(6.071.13) 73.81.6413.85.36 66.868.661.34 0.2516.2
11、4,66.868.661.34 0.2516.24 (1.250.125)8 3.6102 3.723.56.283.5 36.83.96.1 15.613.115.615.62.1 4.87.8780.52,324.90.9 4.8100.1 56.59.956.5 7.0910.80.87.09 25.48(9.40.52) 18.769.918.76 3.94.16.15.9,6.94.83.1 0.4566.223.78 15.894.025.40.98 5.171.83.2 13.75(3.756.48) 3.687.562.68 7.852.340.854.66 35.61.815
12、.67.2 3.822.90.189.1 9.64.83.6,7.140.532.47 5.272.860.661.63 13.354.682.65 73.81.6413.85.36 47.87.45+8.8 0.398+0.36+3.64 15.75+3.590.59+14.25,4.5X 3.6+5.2X0.35 6.15X9.4 4.2 4.5X0.9+5.5X0.9 7.8+4.56+2.2 1.3+4.7X0.9 5.01 - 1.9 + 4.99 0.4X99 + 0.4 7.5 - 7.5 X 0.8,2.557.1+2.457.1,3.94.16.15.9 5.8324.27,
13、比比看，谁算的快又准 6.210= 3.12100= 9.210= 6.44100 = 7.011000 = 23.11000= 0.045 100= 0.4510 = 0.00451000 3.4210=,0.710= 2.810= 0.0510= 29.8100= 1.275100= 0.25100= 271000= 3.721000= 0.31000= 5.931000=,二、概念类,1、在下图中标出 0.01, 0.09, 0.15 ,0.21, 并写出图上字母表示的数。,0 0.1 0.2 0.3,2. 在（ ）里填合适的小数。,小数的意义：,十分之几,一位小数,十分之一,百分之几,两位小数,千分之几,三位小数,百分之一,千分之一,0.1,0.01,0.001,计数 单位:,0.1表示把1平均分成10份，其中的一份 就是十分之一，可以写作0.1。,意义：,3 . 4 1 8,0 . 6 0 2,2个1，3个0.1，4个0.01，组成（ ）。,十分位是6，千分位上是5，这个数是（ ）。,0.26可以写作（ ），有（ ）个0.01,5.02里面有（ ）个0.01,1里面有（ ）个0.1,1
