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If x + 3y = 5 and 3x + y = 7, then x + y =

If x + 3y = 5 and 3x + y = 7, then x + y =
(A)    1
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Nova Math - Problem Set P: Equations

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Posted: 10/28/2012 20:02
Why were the two added? Because we are looking for x+y?
Thanks
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Posted: 10/28/2012 22:22
Mona, yes. You kind of have to look for what the question is asking. Since we can scan the units of x and y in each equation and they are (1 and 3) and (3 and 1), we decide if we add the equations, the will add up to 4 and 4, and we can easily divide the resulting equation by 4 to get x + y.

Alternatively we could solve for x and y through substitution or elimination (remember how to solve 2 algebraic equations with 2 unknowns). It will take longer for the purpose of this question.
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