# Homework Help: Problem solving with quadratic functions.

1. Sep 16, 2011

### davie08

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. Sep 16, 2011

### ArcanaNoir

the clue here is "depends". Since q depends on p, p is the independent variable, which is always x.

3. Sep 16, 2011

### davie08

okay thanks that makes sense.