下面各题,怎样算简便就怎样算
(-)×
×+××19+××13×11×+×-2008×(+)×7×95-3×+-(-+)
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解:(1)(-)×,
=×-×,
=1-,
=;
(2)×+×,
=×(+),
=1,
=;
(3)×19+,
=×(19+1),
=×20,
=13;
(4)××13×11,
=(×11)×(×13),
=10×1,
=10;
(5)×+×-,
=×(+-1),
=×1,
=;
(6)2008×,
=(2007+1)×,
=2007×+1×,
=2006+,
=2006;
(7)(+)×7×9,
=(+)×(7×9),
=(×7×9)+(×9×7),
=(4×9)+(2×7),
=36+14,
=50;
(8)5-3×+,
=5-+,
=5-(-),
=5-,
=2;
(9)-(-+),
=-+-,
=(1+)-(+),
=2-1,
=1.
解析分析:(1)(2)(3)(5)运用乘法分配律简算;
(4)运用乘法交换律和结合律简算;
(6)先把2008分解成2007+1,再运用乘法分配律简算;
(7)先把7×9结合在一起,再运用乘法分配律简算;
(8)先算乘法,再根据加法结合律简算;
(9)运用加法结合律和减法的性质简算.
点评:此题是考查四则混合运算,要仔细观察算式的特点,灵活运用一些定律进行简便计算.