SOLUTION: Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 250 boxes. But when you raise your price to $4 you only sell 120 boxes. a. Write an equation f

Question 515003: Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 250 boxes. But when you raise your price to $4 you only sell 120 boxes.
a. Write an equation for the number of boxes you sell as a function of the price you charge.
b. Denote "B" for number of boxes, and "P" for the price you charge.
c. Assume the function is linear
Found 2 solutions by richwmiller, josmiceli:
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!

B=-130P+640
the two points will be
P,B
3, 250
4, 120
slope will be 250-120/3-4
130/-1
-130
b=mp+y
120=-130*4+y
120=-520+y
120+520=y
640=y
b=-130p+640
check
250=-130*3+640
250=-390+640
250=640-390
250=250
ok
120=-130*4+640
120=640-520
120=120
ok
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = number of boxes
Let = price charged
Assume a straight line
The data given tells what the slope of the line is.
Plot on the vertical axis
Plot on the horizontal axis
slope =
slope =
The equation so far is:

Where is the vertical intercept
Plugging in data:

The equation is:

check answer:

( error due to rounding off)
and

( also round-off error )
Here's the plot:

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