题目内容

数学公式8.16-3.875-2.125-1.16
(0.25×4-0.25×3)×40数学公式
9999×7778+3333×6666(29×0.48-4.77+29×0.52-5.23)×99.

解:(1)78.5+1586-21+414,
=(78.5+21)+(1586+414),
=100+2000,
=2100;

(2)8.16-3.875-2.125-1.16,
=(8.16-1.16)-(3.875+2.125),
=7-6,
=1;

(3)(0.25×4-0.25×3)×40,
=[0.25×(4-1)]×40,
=(0.25×1)×40,
=0.25×40,
=10;

(4)-(+),
=--
=1-
=

(5)9999×7778+3333×6666,
=9999×7778+9999×2222,
=9999×(7778+2222),
=9999×10000,
=99990000;

(6)(29×0.48-4.77+29×0.52-5.23)×99,
=(29×0.48+29×0.52-5.23-4.77)×99,
=[29×(0.48+0.52)-(5.23+4.77)]×99,
=[29×1-10]×99,
=19×99,
=19×(100-1),
=19×100-19×1,
=1900-19,
=1881.
分析:(1)根据加法交换律和结合律简算;
(2)根据减法的性质简算;
(3)先把小括号里面的运算运用乘法分配律简算,再算括号外的乘法;
(4)根据减法的性质简算;
(5)先把3333×6666根据积不变规律变成9999×2222,再运用乘法分配律简算;
(6)综合运用加法结合律、减法的性质以及乘法分配律简算.
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.
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