题目内容

口算下面各题.
1
3
-
1
5
=
1
4
+
3
5
=
7
8
-
1
2
=
1
4
=
7
10
×6=
8
9
÷
8
10
=
1
3
×6=
3
8
×
1
4
=
2
3
-
1
4
=
1
6
÷
1
3
=
1
2
÷
3
4
=
8
19
×
5
16
=
1
4
×
4
10
=
7
12
÷
7
4
=
5
7
÷
10
21
=
6.4÷0.08= 4-2.92=
7
9
÷
6
7
=
分析:(1)(2)(3)(9)通分计算;(4)(6)(10)(11)(14)(15)(18)把除法改为乘法,再计算;(5)(7)(8)(12)(13)属于分数乘法,该约分的要约分;(16)把被除数和除数分别扩大100倍,再相除;(17)注意数位对齐.
解答:解:
1
3
-
1
5
=
2
15
;   
1
4
+
3
5
=
17
20
;    
7
8
-
1
2
=
3
8
;      2÷
1
4
=8;       
7
10
×6=
21
5
;     
8
9
÷
8
10
=
10
9

1
3
×6=2;         
3
8
×
1
4
=
3
32
;    
2
3
-
1
4
=
5
12
;    
1
6
÷
1
3
=
1
2
;       
1
2
÷
3
4
=
2
3
;      
8
19
×
5
16
=
5
38

1
4
×
4
10
=
1
10
;      
7
12
÷
7
4
=
1
3
;   
5
7
÷
10
21
=
3
2
;    6.4÷0.08=80;   4-2.92=1.08;    
7
9
÷
6
7
=
49
54
点评:此题考查了分数的乘法和除法,以及小数的除法和减法,根据题目特点,灵活解答.
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