题目内容

(2009?湛河区)脱式计算,能简算的要简算.
(1)0.6+6×32×0.25                    
(2)(
4
5
+
1
4
)
÷
7
3
-
1
4

(3)36×(
7
9
+
1
4
-
5
6
)                    
(4)
8
9
×[
7
8
-(
7
16
+
1
8
)].
分析:(1)把32分解成8×4,然后用乘法结合律简算;
(2)先算小括号里面的加法,再算括号外的除法,最后算减法;
(3)运用乘法分配律简算;
(4)先去掉小括号,再把中括号里面的运算用加法交换律简算,最后算括号外的乘法.
解答:解:(1)0.6+6×32×0.25,
=0.6+(6×8)×(4×0.25),
=0.6+48×1,
=0.6+48,
=48.6;

(2)(
4
5
+
1
4
)
÷
7
3
-
1
4

=
21
20
×
3
7
-
1
4

=
9
20
-
1
4

=
1
5


(3)36×(
7
9
+
1
4
-
5
6
),
=36×
7
9
+36×
1
4
-36×
5
6

=28+9-30,
=7;

(4)
8
9
×[
7
8
-(
7
16
+
1
8
)],
=
8
9
×[
7
8
-
7
16
+
1
8
],
=
8
9
×[
7
8
+
1
8
-
7
16
],
=
8
9
×[1-
7
16
],
=
8
9
×
9
16

=
1
2
点评:运算定律是常用的简便运算的方法,要熟练掌握,灵活运用.
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