31.8*7.9+12.5*5.9+44.3*2.1用简便方法计算
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31.8*7.9+12.5*5.9+44.3*2.1
=31.8*7.9+12.5*5.9+（31.8+12.5）*2.1
=31.8*7.9+12.5*5.9+31.8*2.1+12.5*2.1
=31.8*7.9+31.8*2.1+12.5*5.9+12.5*2.1
=31.8*（7.9+2.1）+12.5*（5.9+2.1）
=31.8*10+12.5*8
=318+100
=418
=31.8*7.9+12.5*5.9+（31.8+12.5）*2.1
=31.8*7.9+12.5*5.9+31.8*2.1+12.5*2.1
=31.8*7.9+31.8*2.1+12.5*5.9+12.5*2.1
=31.8*（7.9+2.1）+12.5*（5.9+2.1）
=31.8*10+12.5*8
=318+100
=418
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