7.25*687.5-725*58.75怎样算简便

7.25*687.5-725*58.75
=72.5*68.75-72.5*58.75*10
=72.5*[68.75-(58.75+58.75*9)]
=72.5*[68.75-58.75+58.75*9]
=72.5*[10-528.75]
=725-72.5*728.75
=-37609.375
这题用的是结合律.结合律的一个好处是,让我们把多个积的形式化为一个积,这样工作量就相对减少.

72.5*68.75-72.5*5875

7.25*687.5-725*58.75
=72.5*68.75-72.5*58.75*10
=72.5*[68.75-(58.75+58.75*9)]
=72.5*[68.75-58.75+58.75*9]
=72.5*[10-528.75]
=725-72.5*728.75
=-37609.375