问题 解答题

用简便方法计算下列各题,并说说所应用的运算定律.

(1)78×92+78×8

(2)127×24-24×27

(3)(25+20)×4

(4)(125-30)×80

(5)39×56+56×56+5×56

(6)24×45-45×9+85×45

(7)43×99

(8)207×101.

答案

(1)78×92+78×8,

=78×(92+8),

=78×100,

=7800;

(2)127×24-24×27,

=(127-27)×24,

=100×24,

=2400;

(3)(25+20)×4,

=25×4+20×4,

=100+80,

=180;

(4)(125-30)×80,

=125×80-30×80,

=10000-2400,

=7600;

(5)39×56+56×56+5×56,

=(39+56+5)×56,

=100×56,

=5600;

(6)24×45-45×9+85×45,

=45×(24-9+85),

=45×100,

=4500;

(7)43×99,

=43×(100-1),

=43×100-43,

=4300-43,

=4257;

(8)207×101,

=207×(100+1),

=207×100+207,

=20700+207,

=20907.

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