SOLUTION: solve equation using substitution X = y + 8 5x + 3y =12 so I put x in 5x = 5(y+8)+3y=12 = 8y + 40 = 12 now I subtract 40 and get 8y=-28 which give me -28/8 or y= -7/2, so when I

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: solve equation using substitution X = y + 8 5x + 3y =12 so I put x in 5x = 5(y+8)+3y=12 = 8y + 40 = 12 now I subtract 40 and get 8y=-28 which give me -28/8 or y= -7/2, so when I      Log On


   

Question 837118: solve equation using substitution
X = y + 8
5x + 3y =12
so I put x in 5x = 5(y+8)+3y=12 = 8y + 40 = 12 now I subtract 40 and get 8y=-28 which give me -28/8 or y= -7/2, so when I plug into y what is my answer for X. the teacher said they a reasonable solution. But I am lost, my dad says no solution, I don't really know. Im in 8th grade algebra
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Clarifying what you tried to do:
X%3C%3Ex.
Choose which way you are using in any given problem and use the variable consistently.
x=x and X=X, but x%3C%3EX and X%3C%3Ex.

Your given system:
x=y%2B8 and 5x%2B3y=12;
Most of what you show looks good.
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You have a formula for x as one of the given equations.
Substitute...
5%28y%2B8%29%2B3y=12
5y%2B40%2B3y=12
8y%2B40=12
8y=12-40
8y=-28
2y=-7
highlight%28y=-7%2F2%29 just as you found. (You showed one arithmetic mistake, like you intended division by 4 but wrote division by 8).
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Use the value for y to find the value of x, from your original first equation:
x=y%2B8
x=-%287%2F2%29%2B8
x=-%287%2F2%29%2B8%282%2F2%29
x=-%287%2F2%29%2B16%2F2
highlight%28x=9%2F2%29
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SUMMARY OF ANSWER RESULTS: x=9%2F2 and y=-%287%2F2%29.