72.8×0.9+ 7.28=72.8×0.9+72.8×0.1=72.8×(0.9+0.1)=72.8×1=72.8
72.8X（0.9+0.1）＝72.8求采纳
72.8*0.9+7.28=72.8*0.9+72.8*0.1=72.8*（0.9+0.1）=72.8*1=72.8
