设60%x克,90%y克x+y=300y=300-x纯酒精是60%*x+90%*y所以60%*x+90%*y=300*70%0.6x+0.9y=210y=300-x0.6x+270-0.9x=2100.3x=60x=200y=300-x=100所以60%要200克,90%要100克