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# whats the answer to x+y=70 over x-y=24 in systems of equations substatutional

its the systems of equation except its the substitutional method

### 1 Answer by Expert Tutors

Charles K. | Charles K - Algebra 1 and Pre-AlgebraCharles K - Algebra 1 and Pre-Algebra
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Hi Rick,

Not quite sur what you are really asking, so I will answer what I think your question could be asking.

If you are asking "How to solve by substitution", then you do three main things:  (1) you simply pick one equation, and then isolate one of the variables in that equation.  So let's take the 1st equation you gave, and let's isolate the y by subtracting x from both sides of that equation.  So instead of x + y = 70, you do this:  ( x - x ) + y = 70 - x.  We are left with  y = 70 - x.

(2) Now since you have a new eauation saying what y = , we can take that thing that y = , which is 70 - x, and replace (substitute) the "y" in the second equation you gave, with the 70 - x, since they are equal. So when you do that , instead of x - y = 24, we now have x - ( 70 - x ) = 24.

(3) Solve this new equation, and we will find what x = .  Once we know x, we can take that number, and replace that number into the y = 70 - x equation to find y.  So x - ( 70 - x ) = 24 becomes  x - 70 + x = 24, and then 2x - 70 = 24.  Move the 70 to the other side of the equals and divide both sides by 2, and we see that (70 + 24) / 2 = 47.  Take that 47, replace that into the x position in y  70 - x, and you get y = 70 - 47, or y = 23.

Check you work by plug-n-check, and you will see that you have your answer.