题目内容

(2012?景洪市模拟)脱式计算
3
8
÷[(
1
5
+
1
4
)×
3
8
]
3
5
-
4
5
×
1
6
÷
3
5

7
20
÷〔
7
11
×(5-
4
3
)〕
1
2
+
1
3
)÷
5
8
-
1
3

76.9÷[1÷(3.1-3.09)]
(0.72+6.58÷0.7)×0.5.
分析:(1)先算加法,再算乘法,最后算除法;
(2)先算乘法,再算除法,最后算减法;
(3)先算减法,再算乘法,最后算除法;
(4)先算加法,再算除法,最后算减法;
(5)先算小括号里面的减法,再算中括号里面的除法,最后算括号外面的除法;
(6)先算除法,再算加法,最后算乘法.
解答:解:(1)
3
8
÷[(
1
5
+
1
4
)×
3
8
]
=
3
8
÷[
9
20
×
3
8
]
=
3
8
×
160
27

=
20
9


(2)
3
5
-
4
5
×
1
6
÷
3
5

=
3
5
-
2
15
÷
3
5

=
3
5
-
2
9

=
17
45


(3)
7
20
÷[
7
11
×(5-
4
3
)]
=
7
20
÷[
7
11
×
11
3
]
=
7
20
×
3
7

=
3
20


(4)(
1
2
+
1
3
)÷
5
8
-
1
3

=
5
6
×
8
5
-
1
3

=
4
3
-
1
3

=1;

(5)76.9÷[1÷(3.1-3.09)]
=76.9÷[1÷0.01]
=76.9÷100
=0.769;

(6)(0.72+6.58÷0.7)×0.5
=(0.72+9.4)×0.5
=10.12×0.5
=5.06.
点评:计算注意搞清运算顺序,并结合数字特点选用适当的方法简算.
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