0.5x+0.4y+18z+3w=100 5x+4y+180z+30w=1000x+y+z+w=100 5x+5y+5z+5w=500-y+175z+25w=500 令y=25a 175z+25w-25a=500 7z+w-a=20z，w，y，x1 22 75 21 21 50 28
