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Simple Linear Equation?

  1. Jul 8, 2010 #1
    1. The problem statement, all variables and given/known data
    P = -50Qd + 80
    P = 2Qs + 10

    P = Price
    Qd = Quantity demanded
    Qs = Quantity supplied

    Find the equilibrium Price and Quantity.

    2. Relevant equations
    Qd = Qs

    3. The attempt at a solution
    Qd = Qs

    Since they both equal to P

    -50Q + 80 = 2Q + 10 [-2Q]
    -52Q + 80 = 10 [-80]
    -52Q = -70 [/52Q]
    Q = 70/52
    Equilibrium Quantity = 70/52

    I don't know why this is wrong?
  2. jcsd
  3. Jul 8, 2010 #2
    I came up with the same answer. I didn't major in economics, though...I just assumed (because it sounds right) that you are right, that equilibrium occurs when the supply = demand.
  4. Jul 8, 2010 #3


    Staff: Mentor

    Are you sure that you are starting with the right equations? Have you given the problem exactly as it appears in your text or wherever you got it? I'm especially concerned with your Qd equation with the -50 coefficient.
  5. Jul 22, 2010 #4
    are you sure that this equation has 2Qs or should it have 20Qs.
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