Posted by steve on .
x+y+z=30
xyz=8
xy+2z=17
x is the same in all equations
y is the same in all equations
z is the same in all equations

algebra 
Reiny,
Add the first and the second > 2x = 39
x = 19
add the first and the third > 2x + 3z = 47
38 + 3z = 47
z = 3
now put those values back into the second
19  y  3 = 8
y = 8 
algebra 
steve,
i am 50 years old, i am sorry but i need this spelled out for me if possible

algebra 
Reiny,
Well Steve, I am 68 years old, lol
I assume you are solving these equations?
x + y + z = 30  first equation
x  y  z = 8 second equation
2x + 0 + 0 = 38  I added them
x = 19 divided by 2, we now know x
x + y + z = 30  first equation again
x  y + 2z = 17 third equation
2x + 0 + 3z = 47  added them
2x + 3z = 47 , but we know x = 19 so..
38 + 3z = 47
3z = 47  38
3z = 9
z = 3 , so now we have x=19 and z=3
let's put this back into the first, or any one really
x + y + z = 30
19 + y + 3 = 30
y + 22 = 30
y = 3022
y = 8
so x=19, y=8, and z=3
notice those values work in all 3 equations. 
algebra 
steve,
Reiny,thanks so much for your help on this!!!!!!!!!!!