设每盒进价x0.2x*50-(2400/x-50)*5=350即10x-12000/x+250=35010x-12000/x=100x-1200/x=10x²-10x-1200=0(x+30)(x-40)=0解得x=40或x=-30(不合）答：每盒进价40元
45.5
