# Free market: supply and demand graph

• Nov 11th 2009, 06:51 PM
dkpeppard
Free market: supply and demand graph
I need to graph this question out to obtain further information to answer the rest of the question.

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?

To find the graph, can I rewrite this in a slope-intercept form? For example, would I assume 'S' and 'D' really are 'y', then work the problem in a slope-intercept form from there?

• Nov 12th 2009, 01:12 AM
BabyMilo
Quote:

Originally Posted by dkpeppard
I need to graph this question out to obtain further information to answer the rest of the question.

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?

To find the graph, can I rewrite this in a slope-intercept form? For example, would I assume 'S' and 'D' really are 'y', then work the problem in a slope-intercept form from there?

d) The price at which supply and demand are equal is called the equilibrium price. What is the equilibrium
price?

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

5000+200x=9500-100x

then solve for x.

and yes you can use the slope-intercept
• Nov 12th 2009, 01:19 AM
BabyMilo
Quote:

Originally Posted by dkpeppard
I need to graph this question out to obtain further information to answer the rest of the question.

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?

To find the graph, can I rewrite this in a slope-intercept form? For example, would I assume 'S' and 'D' really are 'y', then work the problem in a slope-intercept form from there?

b) What happens to the supply as the price increases?
c) What happens to the demand as the price increases?

b) there would be excess or surplus supply
c) there would be excess or surplus demand

i think that's what you need. correct if im wrong anyone.
• Nov 12th 2009, 06:25 AM
dkpeppard
Babymilo,

Thanks for the help. I will look at this more in a bit. I have a meeting I am off to for now.
• Nov 12th 2009, 11:47 AM
dkpeppard
Quote:

Originally Posted by BabyMilo
d) The price at which supply and demand are equal is called the equilibrium price. What is the equilibrium
price?

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

5000+200x=9500-100x

then solve for x.

and yes you can use the slope-intercept

Thanks. I am trying to figure out the graph points now.

I worked 'd' out as follows:

5000+200x=9500-100x
5000+200x+100x=9500
5000+300x=9500
300x=4500
X=15
• Nov 12th 2009, 12:33 PM
dkpeppard
Ok, maybe a little more help here, please.

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?
• Nov 12th 2009, 01:24 PM
BabyMilo
Quote:

Originally Posted by dkpeppard
Ok, maybe a little more help here, please.

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?

not quite sure what u are saying but here the graph:

and where they cross is your x=15 and y=8000 where they are in equilibrium.

so your answer to d) is 8000unit or \$8000 if you are in the US.
• Nov 12th 2009, 01:34 PM
dkpeppard
Quote:

Originally Posted by BabyMilo
not quite sure what u are saying but here the graph:

and where they cross is your x=15 and y=8000 where they are in equilibrium.

so your answer to d) is 8000unit or \$8000 if you are in the US.

Thank you very much for help on the graphing. (Nod)

Using what you listed in post number 5, I worked the equilibrium out to be x=15. Wouldn't the answer to 'd)' be \$15?
• Nov 12th 2009, 01:49 PM
BabyMilo
Good Question but almost 99% or even 100% of the supply and demand graphs have y=price and x=Qty of sold of a product. So no, it's not 15, it's 8000. :)

See Supply and demand - Wikipedia, the free encyclopedia for more info.
• Nov 12th 2009, 01:50 PM
BabyMilo
When you worked out x=15

you have to sub x into one of the equation (S=5000+200x, D=9500-100x), to find out price.

so you would put x into S=5000+200x for example, which turns out to be 8000 which is your answer and it works with D=9500-100x as well.
• Nov 13th 2009, 06:49 AM
dkpeppard
Quote:

Originally Posted by BabyMilo
When you worked out x=15

you have to sub x into one of the equation (S=5000+200x, D=9500-100x), to find out price.

so you would put x into S=5000+200x for example, which turns out to be 8000 which is your answer and it works with D=9500-100x as well.

Ok, thank you for explaining. I guess I forgot the step of plugging 'x' back into the equation to get the actual value for 'S' and 'D'.