解:
(1)(
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+
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)÷(0.5-0.2),
=0.7÷0.3,
=
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;
(2)18÷[5.2÷(
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-
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+
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)]÷
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,
=18÷[5.2÷(
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+
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)]÷
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,
=18÷[5.2÷
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]÷
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,
=18÷6÷
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,
=3÷
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,
=10.5;
(3)(
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-
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-
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)÷
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,
=(
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-
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-
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)×48,
=
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×48-
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×48-
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×48,
=36-4-2,
=30;
(4)(999×1.01+9.9×99.9)÷5×
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,
=(99.9×10.1+9.9×99.9)÷5×
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,
=99.9×(10.1+9.9)÷5×
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,
=99.9×20÷5×
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,
=1998÷5×
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,
=399.6×
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,
=66.6.
分析:(1)先算小括號(hào)里面的加法和減法.再算除法;
(2)先算小括號(hào)里面的,再算中括號(hào)里面的除法,再按照從左向右的順序進(jìn)行計(jì)算;
(3)根據(jù)乘法分配律進(jìn)行計(jì)算;
(4)根據(jù)乘法分配律進(jìn)行計(jì)算.
點(diǎn)評(píng):考查了運(yùn)算定律與簡(jiǎn)便運(yùn)算,四則混合運(yùn)算.注意運(yùn)算順序和運(yùn)算法則,靈活運(yùn)用所學(xué)的運(yùn)算律簡(jiǎn)便計(jì)算.