60x=1000+y(1) 40x=1000-y (2) (1)式加(2)式可得: 60x+40x=1000+1000+y-y 100x=2000 x=2000/100=20 将x=20代入(1)得: 60*20=1000+y y=60*20-1000 =1200-1000 =200
60x-1000=1000-40x60x+4Ox=1OOO+100O1OOx=2000x=20