题目内容

脱式计算:
0.75÷0.25+
3
4
×
2
3
       
(8.6×0.5-
31
10
)÷12      
39
10
÷[
15
4
-(
4
3
+
1
6
)]
[800×(1+25%)-360×1.5]÷25%      
15-[
4
3
+(2.5-
7
3
)]÷0.125.
分析:这6个算式都按照分数的四则混合运算的顺序进行计算,有括号的先计算括号内部的,再计算括号外部的,第⑥个式子再计算时多留心计算即可正确解答.
解答:解:①0.75÷0.25+
3
4
×
2
3

=
3
4
×4+
3
4
×
2
3

=3+
1
2

=3.5;

②(8.6×0.5-
31
10
)÷12,
=(4.3-3.1)÷12,
=1.2÷12,
=0.1;

39
10
÷[
15
4
-(
4
3
+
1
6
)],
=
39
10
÷[
15
4
-
3
2
],
=
39
10
÷
9
4

=
39
10
×
4
9

=1
11
15


④[800×(1+25%)-360×1.5]÷25%,
=[800×
125
100
-360×1.5]×4,
=[1000-540]×4,
=460×4,
=1840;

⑤15-[
4
3
+(2.5-
7
3
)]÷0.125,
=15-[
4
3
+
5
2
-
7
3
]÷
1
8

=15-[
8
6
+
15
6
-
14
6
]×8,
=15-
3
2
×8

=15-12,
=3.
点评:考查了运算定律与简便运算,四则混合运算.注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
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