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Homework Help: Problem solving with quadratic functions.

  1. Sep 16, 2011 #1
    1. The problem statement, all variables and given/known data
    okay I know understand that I should get a reasonable understanding about the questions I post before I post them sorry about before.

    An Illinois farmer will plant from 800 to 2000 acres of soybeans. The number of acres q that he will plant depends on the selling price per bushel p that is being paid in April. Suppose that if p=$10, then all 2000 acres will be planted, but if p=$6.25, then only 800 acres will be planted.

    a)Assuming p and q are linearly related, find q as a function of p, giving a suitable domain.


    2. Relevant equations



    3. The attempt at a solution

    for some reason this question seems to work out to be the opposite of what I've been doing with my other word problems, heres what I tried.

    (2000,10) and (800,6.25)


    m=6.25-10/800-2000 = .003125

    q-q1 = m(p-p1)

    q-2000 = .003125(p-10)

    q-2000 = .003125p - .03125

    q= .003125p + 1999.96875 800<q<2000


    so this is the wrong answer and to get the right answer I have to make p my x and q my y. Then for the domain you find what it is for price.

    But I just saw a tutor and she has it on a formula sheet that x=q and p=y.
     
  2. jcsd
  3. Sep 16, 2011 #2
    the clue here is "depends". Since q depends on p, p is the independent variable, which is always x.
     
  4. Sep 16, 2011 #3
    okay thanks that makes sense.
     
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