【简便算法①】：
81.9×0.9-0.9×1.9
=(81.9-1.9)×0.9
=80×0.9=8×9
=72
【简便算法②】：
81.9×0.9-0.9×1.9
=(80+1.9)×0.9-1.9×0.9
=80×0.9+1.9×0.9-1.9×0.9
=72
----------------------------------------------------------------------------------------------------------------------
采纳是我前进的动力~
如果您觉得满意,可以点击“采纳为满意答案”哦!