www.qcfz.net > 77+78+79+80+81+82+83用乘法怎么算

77+78+79+80+81+82+83用乘法怎么算

75+76+77+78+79+80+81+82+83=(75+83)(83-75+1)/2=711

74+75+76+77+78+79 =76.5-2.5+76.5-1.5+76.5-0.5+76.5+0.5+76.5+1.5+76.5+2.5 =76.5×6+(2.5+1.5+0.5-0.5-1.5-2.5) =76.5×6 =459

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