SOLUTION: The quantity demanded for a certain brand of portable CD players is 200 units when the unit price is set at $90. The quantity demanded is 1200 units when the unit price is $40. Fin

Question 701268: The quantity demanded for a certain brand of portable CD players is 200 units when the unit price is set at $90. The quantity demanded is 1200 units when the unit price is $40. Find the demand equation and sketch its graph. THANKS
Found 2 solutions by josmiceli, stanbon:
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Plot quantity demanded on the vertical axis
and unit price on the horizontal axis.
Let = quantity demanded
Let = unit price
------------------
I can write a general point-slope formula:

--------------------
check answer:
Does it go through ( 90, 200 ) ?

OK
Does it go through ( 40, 1200 ) ?

OK
Here's the plot:

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The quantity demanded for a certain brand of portable CD players is 200 units when the unit price is set at $90. The quantity demanded is 1200 units when the unit price is $40. Find the demand equation and sketch its graph.
---
You have two points: (90,200) ; (40,1200)
-------
slope = (1200-200)/(40-90) = -1000/50 = -20
------
D(x) = -20x + b
Solve for "b":
200 = -20*90 + b
b = 200 + 1800
b = 2000
-----
Equation:
D(x) = -20x + 2000 where x is the price per unit.
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Cheers,
Stan H.
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