Solve By The Elimination Method. X + Y = 15, 4x - Y = 20 Type An Ordered Pair?

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Oddman answered
Add the two equations to eliminate y.
  (x + y) + (4x - y) = (15) + (20)
  5x = 35    (collect terms)
  x = 7    (divide by 5)

Subtract 4 times the first equation from the second equation to eliminate x.
  (4x - y) - 4(x + y) = (20) - 4(15)
  -5y = -40    (collect terms)
  y = 8    (divide by -5)
The solution is (x, y) = (7, 8).
After you have a value for one of the variables, it is often more convenient to solve for the other using substitution.
  7 + y = 15    (substitute the value of x into the first equation)
  y = 8    (subtract 7 from both sides)

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