6年级数学题43

x+y+z=142 ......................(1)
x/28+y/30+z/35=4.5 .............(2)
x/35+y/30+z/28=4+42/60=4.7.......(3)

(3)-(2):7/(28*35)*(z-x)=0.2
z-x=28...........................(4)
(1)-(2)*30:-2x/28+5z/35=7
-x+2z=98
2z-x=98.........................(5)
(5)-(4):z=70
代入(4):x=z-28=42
代入(1):42+y+70=142,y=142-42-70=30
所以,
x=30
y=42
z=70