Respuestas

2013-12-11T04:53:47+01:00
1........x+y+z=65
2........x=2y

65-(x+y)=z
x+y=65-z

3.......20x+5y+10z=875
20(2y)+5y+10z=875
45y+10z=875

z=(875-45y)/10

2y+y+(875-45y)/10=65

30y+875-45y=650

-15y=-225
y=15
x=30
z=20