解:(1)2005-999,
=2005-(1000-1),
=2005-1000+1,
=1006;
(2)0.25+
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,
=0.25+0.2-0.45,
=0;
(3)
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,
=0.72÷0.75×2,
=2;
(4)
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,
=(
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+
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-
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)×3,
=
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×3+
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×3-
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×3,
=
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+1-
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,
=0.3;
(5)
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,
=[(99
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+
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)-(29
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+30
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)]×
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,
=40×
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,
=4;
(6)
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,
=
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×

×
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×9,
=
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;
(7)11×991+99,
=11×991+11×9,
=11×(991+9),
=11000;
(8)
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,
=
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,
=
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,
=1;
(9)1+3+5+7+9+11+13+15+17+19,
=(1+19)+(3+17)+(5+15)+(7+13)+(9+11),
=20×5,
=100;
(10)
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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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.
分析:(1)把999看作1000,然后加1;
(2)、(3)把分?jǐn)?shù)都化為小數(shù),進(jìn)行計(jì)算;
(4)先根據(jù)除以一個(gè)分?jǐn)?shù),等于乘這個(gè)分?jǐn)?shù)的倒數(shù),然后運(yùn)用乘法分配律進(jìn)行解答;
(5)先把括號(hào)里的運(yùn)算進(jìn)行交換,再結(jié)合,進(jìn)行簡(jiǎn)算,然后再和
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相乘;
(6)按照乘除法計(jì)算方法進(jìn)行解答;
(7)把99分解成11×9,然后運(yùn)用乘法分配律進(jìn)行簡(jiǎn)算;
(8)先算1-
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=

,再算1÷
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=4,繼而算5-4=1,最后算1÷1=1;
(9)首位進(jìn)行結(jié)合,再運(yùn)用乘法分配律進(jìn)行解答;
(10)分別算出括號(hào)里的,然后相乘,進(jìn)行約分,即可.
點(diǎn)評(píng):解答此題的關(guān)鍵:熟練掌握加、減、乘、除中的一些運(yùn)用定律和性質(zhì),能根據(jù)數(shù)的特點(diǎn),運(yùn)用簡(jiǎn)便方法,進(jìn)行簡(jiǎn)算.