## Free market: supply and demand

Simple patterns, variables, the order of operations, simplification, evaluation, linear equations and graphs, etc.
dkpeppard
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Joined: Thu Nov 12, 2009 3:30 pm
Location: Denver, CO
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### Free market: supply and demand

Hello everyone. My first post here.

I have this problem I am trying to work through, please.

Free market. The equations S=5000+200x and D=9500-100x express the supply S and the
demand D, respectively, for a popular compact disc brand in terms of its price x (in dollars).

a) Graph the equations on the same coordinate system.
b) What happens to the supply as the price increases?
c) What happens to the demand as the price increases?
d) The price at which supply and demand are equal is called the equilibrium price. What is the equilibrium
price?

I have already figured out 'd)' as x = 15. I reached this conclusion by:

Since S=5000+200x and D=9500-100x

5000+200x=9500-100x
5000+200x+100x=9500
5000+300x=9500
300x=4500
X=15

I still need to figure out a, b, and c. I know I can use a slope-intercept to figure out the graph using the equation of y=mx+b. This is where I start losing it.
I know that: x = 15. I know the slope-intercept formula is y=mx+b.

Using S=5000+200x, D=9500-100x I would assume these would represent x,y. So, would I assume x=8000, y=8000 and graph them as 8000,8000? So then I would start the problem out as 8000=m(8000)+b?

Your help with the remaining letters is much appreciated.

stapel_eliz
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Joined: Mon Dec 08, 2008 4:22 pm
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a) To learn how to graph linear equations, try here.

b) To learn about "slope" and what it means for a slope to be "increasing" or "decreasing", try here. To learn how to interpret slope in the context of word problems, try here.

c) This one works just like (b).

Note: "When the price increases" means (graphically) "as the x-values get larger".

dkpeppard
Posts: 2
Joined: Thu Nov 12, 2009 3:30 pm
Location: Denver, CO
Contact:

### Re: Free market: supply and demand

Thanks. I will look at the links and try to apply the information you supplied to help solve my problem.