0.31*68+0.68*68+0.68＝31×0.68＋68×0.68+1×0.68＝（31+68+1）×0.68＝100×0.68＝最后一步不用写了吧 ^_^
=0.31*68+0.68*68+0.01*68=(0.31+0.68+0.01)*68=1*68=68
同上
