北师大四年级数学下册小数乘法简便计算.docx
《北师大四年级数学下册小数乘法简便计算.docx》由会员分享,可在线阅读,更多相关《北师大四年级数学下册小数乘法简便计算.docx(30页珍藏版)》请在冰豆网上搜索。
北师大四年级数学下册小数乘法简便计算
四年级下册小数练习题
一、脱式计算,能简算的要简算。
7.8×1.3+0.9
48-1.8
×24
0.25
×0.46×0.4
2.5×1.3+0.9
3.8
×41-3.8
(4+0.4)×2.5
0.27×3.8+0.27×6.2
2.9
×100.1
27.5
×101-27.5
40×0.63×0.25
3.62
×25.7+3.62×74.3
0.25×4.87×4
18.8+23.6+26.4
10.95-3.74-4.26
95.59-
(9.59+12.78)
25.6-(0.23+5.6)-1.77
13.75-(4.75+6.48)
7.83+2.34-0.83+6.66
3.82+2.9+0.18+9.1
5.93+0.19+2.81
25.48-((9.4-0.52)
3.07-0.38-1.62
35.6-1.8-15.6-7.2
7.3+2.7-7.3+2.7
48.4+2.78+51.6-0.78
23.4+0.8-13.4-7.2
4.8+8.63+5.2+0.37
3.25+2.76+1.75
1.27+3.9+0.73+15.1
5.84-1.8-3.2
132.44-(58.74+19.44)7.5+4.8-6.5
7.14-0.53-2.4713.75-(3.75+6.48)
13.45-4.68+2.55
47.8-7.45+8.2
36.8-4.5+6.98
49.8-9.6+8.8
15.2-6.8-3.45
1.76+0.65+3.24
0.134+2.66+0.8
7.5+4.9-6.3
3.45+1.79+0.65
4.85+8.63+0.37
1.76+3.44+0.35
36.54-1.76-8.66
8-2.45-1.02
23.4+3.4-0.23
6.02+3.6+1.98
3.07-0.38-1.62
7.5+4.9-6.5
36.8-3.9-6.88
3.285+1.79+0.59
23.4-0.8+13.4
32+4.9-8.6
1.29+3.7+2.71
5.93+0.49+2.06
9-2.45-1.65
21+0.56+11.3
64.89-7.88-13.6
二、能简便的要简便计算。
12.5×8.2×80.23
×1.4+0.23×8.6
0.125×(80+0.8)
0.4×0.16×2.5
5.6×101
7.85
×99
1.15
×99+1.15
16.2×101-16.2
45
×0.78+5.5×7.8
2.8+7.2×0.81
0.34×2.5×0.4
1.25×11×4×0.8
8.93×5.7+8.93×3.3+8.93
4.82×102
0.7×0.46+0.7×0.545.6-4.34+7.346
85.7-
(15.3-4.8
)
25.4-(15.3+7.7)
3.6
-1.28+3.09
3.8-0.46-1.723
25.6-(0.23+5.6)-1.77
13.75-(4.75+6.48)
7.83+2.34-0.83+6.66
3.8
2+2.9+0.18+9.1
25.48-((9.4-0.52)
35.6-1.8-15.6-7.2
5.93+0.19+2.81
7.3+2.7-7.3+2.7
3+5.2+0.37
3.07-0.38-1.62
48.4+2.78+51.6-0.78
23.4+0.8-13.4-7.2
4.8+8.6
1.27+3.9+0.73+15.1
5.84-1.8-3.2
132.44-(58.74+19.44)
7.5+4.8-6.5
13.45-4.68+2.55
3.25+2.76+1.7513.75-(3.75+6.48)
7.14-0.53-2.47
47.8-7.45+8.2
36.8-4.5+6.98
49.8-9.6+8.8
15.2-6.8-3.45
3.45+1.79+0.65
3.45+1.79+0.65
1.76+0.65+3.24
0.134+2.66+0.8
7.5+4.9-6.3
4.85+8.63+0.37
1.76+3.44+0.35
36.54-1.76-8.66
3.45+1.79+0.65
7.5+4.9-6.5
23.4+3.4-0.23
6.02+3.6+1.98
3.07-0.38-1.62
36.8-3.9-6.88
3.285+1.79+0.59
23.4-0.8+13.4
1.29+3.7+2.7121+0.56+11.332+4.9-8.6
5.93+0.49+2.06
9-2.45-1.65
一、乘法交换律
abcacb
0.25×8.5×412.5×0.96×0.80.25×0.73×40.25×16.2×4
二乘法结合律
(ab)ca(cb)
4.36×12.5×80.95×0.25×435×0.2×0.50.75×50×0.4
三、乘法分配律
(ab)
c
ac
bc
(1.25-0.125)
×8
(20-4)×0.25
(2+0.4)×5
(125+2.5
)×0.8
四、乘法分配律逆应用
a
ba
c
a(bc)
3.72
×3.5+6.28
×3.5
15.6
×2.1-15.6×1.1
3.83×4.56+3.83×5.44
7.09
×10.8-0.8
×7.09
27.5×3.7-7.5×3.7
3.9×2.7+3.9×7.3
10.6
×0.35-9.6
×0.35
7.6×0.8+0.2×7.6
五、把其中一个因数分成两个数的和或差,再按乘法分配律
0.8
×100.1
0.79×99
0.85×199
3.65×10.1
4.6
×0.9
0.65×101
4.8×10.1
3.6×102
0.39
×199
8.9×1.01
0.32×403
3.65×10.1
0.85
×9.9
0.65×101
六、拆分因数
1.25×2.5×323.2×0.25×12.50.25×36
25×4.48.8×1.25
七、添加因数“1”
56.5×99+56.59.7×99+9.74.2×99+4.25.4×11-5.4
1.87×9.9+0.18712.7×9.9+1.27
八、更改因数的小数点位置
6.66×3.3+66.6
×67
46×57+23×86
4.8×7.8+78×0.52
3.14×0.68+31.4×0.032
101×0.87-0.91×87
3.65×4.7-36.5×0.37
2.3
×16+2.3×23+2.3
314×0.043+3.14×7.2-31.4×0.15
5×1.03×0.2
32
×1.25
0.45×99
53×10.1
0.125×96
12.5×10.8
25
×7.3×0.4
45×21-50×2.1
45×1.58+5.5×15.8
4.2
×6.51+3.49×4.2
9.99×2.22+3.33×3.34
三、直接写得数
3.8
×2=
10
×0.7=
13.9
×0=
50.8
×100=
5.5
×1=
1.8
×0.5=
3.2
×3=
13.1
×0.3=
0.08×1.25=
2.5
×4=
2.5
×8=
0.5
×0.2=
0.6
×0.1=
0.7
×0.8=
2.5
×8×0=
125
×0.8=
3.8
×2=
10
×0.7=
13.9
×0=
508
÷100=
5.5
×1=
1.8
×0.5=3.2
×3=
13.1
×0.3=
0.08×1.25=
2.5
×4=
2.5
×8=
0.5
×0.2=
0.6
×0.1=
0.7
×0.8=
2.5
×8×0=
125
×0.8=
四、竖式计算
2.8×0.7=
13×0.15=
0.39
×0.6=0.38×600=
7.05×2.4=
0.46×7.9=
89.3
×7.6=60.5×400=
3.05×18=4.6×18.9=40.5×4.2=0.37×2.31=
3.8
×0.12=
0.57
×0.6=
6.4
×0.5=
6.7
×5.8=9.8
×3.8=
7.8×6.4=
4.6
×2.7=
4.5
×2.7=
5×1.6=3
×0.6=3
×1.2=
6.7
×7.6=
5.4
×7.8=
2.6
×3.6=
3.5
×1.7=
8.3
×2.6=
1.4×0.7=
4.5
×2.8=
7.4
×2.6=
6.2
×1.4=
5.4×2.6=
2.3
×1.4=
3.7
×1.8=
4.5
×2.3=
5.2×1.6=
3.6
×0.8=
0.66
×1.4=
6.5
×5.8=
0.72
×0.49=
0.42
×0.28=
0.24
×0.19=
2.4
×1.3=
0.72×0.27=
0.78
×0.32=
0.65
×0.04=
0.23
×0.16=0.29
×0.15=
0.16×0.19=
4
×1.2=
7
×4.6=6×0.37=
0.28
×0.27=
0.75
×0.42=
2.3
×1.9=
8×0.64=
2.7
×0.8=
10
×4.2=
7.1
×3.9=
4.3×1.4=
2.6
×1.6=
0.8
×0.3=0.65
×0.4=0.91
×0.6=
1.8×1.6=
4.8
×0.5=
3.2
×0.4=
9.8×4.8=
12
×8.3=
15.2
×6.5=
20.1
×11.1=13.34×10.32=
6.52
×0.48=
6.3
×5.1=
8.7
×3.6=
14.3
×4.3=
1.5×0.54=
10
×4.2=
2.47
×3.24=
2.98
×0.56=
5.64
×1.78=
8.02
×0.98=
7.1
×3.9=2.8
×11.39=
12.53×4.67=7.2
×6.45=
1.65
×3.35=
7.96
×1.45=
60
×1.27=
6.07
×4.89=
5
×0.41=
0.9×0.5=
2
×0.7=
1.2
×4.3=
5.4×2.7=
6
×2.9=
3.7
×1.7=
4.2×0.8=7.5×2.5=
2.2
×4.3=
9.5
×7.1=
3.5
×1.6=
5.2
×2.8=
7.8
×1.6=
9.6
×4.1=
10
×4.2=
5.1
×2.5=
4.1
×3.4=
1.2
×3.8=
9.6
×4.1=7.8
×1.6=
3.5
×1.6=
4.4
×1.4=
2.9
×2.1=
3.5
×1.2=
4.8
×3.4=
6.9
×2.5=
2.5
×7.8=
8×5.4=
6.9
×2.5=
2
×3.5=
6.8
×2.2=
4.7
×5.4=
4.1
×8.8=
2.2
×5.5=
9.6
×2.1=
1.7
×3.8=
7.4
×3.6=
0.8
×0.23=
1.6
×2.4=4.7
×3.5=
1.2
×3.6=
1.5
×3.8=
2.8
×1.2=7.3×2.7=
7.3
×2.7=
6.2
×3.7=
4.2
×3.9=
0.54
×0.65=
7.5
×5.2=
0.7
×0.5=
0.32
×0.47=8.3
×6.3=
7.2
×0.42=
0.48
×0.52=
0.8
×0.25=
43.5×0.65=
0.32
×0.16=
0.35
×0.55=
0.87
×0.8=
0.24
×0.08=
0.92
×0.37=
1.4
×0.6=
3.6
×4.2=
0.72
×0.48=
6.8
×3.2=
7.1
×3.4=
0.42
×0.66=0.32
×0.68=
2.8
×7.2=
0.65
×0.19=
3.09
×1.2=
3.25
×5.64=
0.25
×0.47=0.82×0.18=
7.8
×2.4=0.45×0.18=
0.4
×0.16=
8.2
×1.8=0.73
×0.27=
8×3.2=
9.8
×4.8=
3
×2.4=
2.8
×0.9=
1.29
×0.18=
5.1
×0.8=
10
×0.3=
8.9
×4.9=
6.8
×0.7=
8
×0.72=
6.6
×3.4=6.4×1.3=
1.2
×0.8=
7.3
×6.2=
8.7
×3.6=
12.3
×0.7=
0.8
×9.2=
4.7
×1.9=
5.1
×3.9=1.4
×0.6=
3.8
×6.4=
0.6
×7.45=
4.9
×0.1=
4.5
×3.2=
1.8
×0.9=
6.5
×0.5=
10.5
×6.5=
7.5
×0.5=
0.78
×0.28=
12.8
×2.8=
9.6
×2.3=
3.8
×0.12=
0.8
×0.08=
10×7.4=
7.5
×3.2=0.42×0.58=
0.8
×0.15=
2.5
×0.4=
8.2
×2.6=
1.4
×0.7=
2.5
×4.6=
0.5
×9.8=
6.7
×2.6=7.2
×5.9=
8.7
×3.6=
5.69
×2.48=
2.9
×4.1=
9.1
×6.7=
2.03
×1.2=
8.6
×4.9=
1.3
×2.03=
9.46×7.21=
1.56
×2.24=
3.5
×1.25=
0.75
×0.4=20×0.78=
4.8
×4.2=
5.7
×3=
4.9
×1.7=
1.34
×0.8=
2
×0.75=
8.7
×0.03=
0.2
×0.09=
8.5
×2.5=
3.4
×1.4=
0.68
×0.42=
7.82
×7.2=
2×9.1=
0.48×0.52=
8.1
×5.1=
0.78
×0.24=
0.8
×0.18=
0.89
×0.25=
1×0.98=
0.9
×0.1=
1
×0.8=
4.5
×4=
5.6
×4=
5.7
×3.3=
10
×4.4=
6
×6.6=
9.5
×2.7=
1
×0.55=
五、列式计算。
1、甲数是15.24,比乙数多7.6,乙数是多少?
2、3.58加上7.08与5.1的差,和是多少?
六、解决问题。
1、小红用20元钱买文具,买钢笔用去6.7元,买文具盒用去9.8元,还剩下多少
钱?
2、爸爸用两条长度分别是1.27米、1.35米的绳子接起来捆扎报纸。
接口处共用
去绳子0.25米,接好后的绳子有多长?
3、一桶油连桶共重12.65千克,用去一半后,连桶还重6.85千克,原来的桶里
有油多少千克?
二、减法中的巧算
1.
减法的性质:
a-b-c=a-(b+c)
巧算下面各题:
①300-73-27②7.42-(3.42+1.5)
③4723-(723+189)
三、加减混合式的巧算
1.
去括号和添括号的法则
在只有加减运算的算式里,如果括号前面是“+”号,则不论去掉括号或添上括
号,括号里面的运算符号都不变;如果括号前面是“-”号,则不论去掉括号或添上括号,括号里面的运算符号都要改变,“+”变“-”,“-”变“+”,即:
a+(b+c+d)=a+b+c+d
a-(b+a+d)=a-b-c-d
a-(b-c)=a-b+c
2.带符号“搬家”
325+46-125+54
=325-125+46+54
=(325-125)+(46+54)
=200+100
=300
注意:
每个数前面的运算符号是这个数的符号
.如+46,-125,+54.而325前面虽
然没有符号,应看作是+325。
3.找“基准数”法
几个比较接近于某一整数的数相加时,选这个整数为“基准数”。
计算78+76+83+82+77+80+79+85
二、用简便方法计算:
536+(541+464)+459588
+264+148
8996+3458+7546
4995-(995-480)
1870-280-520
4250-294+94
478-128+122-72
464-545+99+345
537-(543-163)-57
947+
(372-447)-572
小数乘法的简便运算
一、乘法交换律与结合律的运用。
提示1:
以下计算中,有的需要把一个小数拆成两个数相乘,要注意拆分后两数
相乘的大小应该与原数相等,特别是小数的位数。
如
3.2=0.8×4
3.2=0.4×8
0.32=0.04×8
0.32=0.08
×4
5.6=0.8
×75.6=0.7×8
0.56=0.07
×80.56=0.08
×7
0.48=0.12
×4
0.48=0.04×12
提示2:
应用乘法结合律解题的口诀是
连乘用结合
提示3:
应用乘法结合律解题的格式是
a×b×c=a×(b×c)最后一个步骤是“×”,
不要看成是“+”.
如2.5×0.48=2.5×0.04×12=0.1×12=1.2
4.56×0.4×2.5
12.5
×2.7×0.8
12.5
×3.2×0.25
2.5×0.48
12.5
×5.6
25
×0.36
乘法分配律的运用。
提示1:
A组中的一个因数都具备一个特点,都接近整数1、10、100等,这样的
数就可以拆分成两个数相加或者相减。
如10.4=(10+0.4)
9.9=(10-0.9)
0.99=(10-0.01)
但也有这样的数8.8=
(8+0.8)4.4=(4+0.4)0.48=(0.4+0.08)
提示2:
应用乘法分配律解题的口诀是
乘加乘减用分配
提示3:
应用乘法分配律解题的格式是(a+b)×c=a×c+b×c最后一个步骤是“+”,不要看成是“×”.
如2.5×0.48=2.5×(0.4+0.08)=2.5×0.4+2.5×0.08=1+0.2=1.2
不是=1+0.2=2
提示4:
应用乘法分配律解题的最后一步,有时是数字比较大的两个数相加减,口算容易出错,这时就要打草稿竖式计算。
0.25×10.412.5
×8.8
9.9
×0.35
3.7×1.8-2.7×1.895.7
×0.28
+6.3×0.28-0.28×2
1.08×9+1.08
比较乘法结合律与分配律在简便运算时的区别。
下面各题用两种方法简算。
12.5×8.812.5×8.80.25×4.8