SOLUTION: 4. Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 200 boxes. But when you raise your price to $4 you only sell 120 boxes. a. Write an equatio

Algebra ->  Linear-equations -> SOLUTION: 4. Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 200 boxes. But when you raise your price to $4 you only sell 120 boxes. a. Write an equatio      Log On


   



Question 492864: 4. Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 200 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 josmiceli, stanbon:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I will plot boxes on the x-axis and cost/box on the y-axis
Us the point-slope formula, which, in general is:

In this case, +x+=+B+ and +y+=+P+
The given points are:
(3,200) and (4,120)
+%28+P+-++120+%29+%2F+%28+B+-+4+%29+=+%28+200+-+120+%29+%2F+%28+3+-+4+%29+
+%28+P+-+120+%29+%2F+%28+B+-+4+%29+=+80+%2F+-1+
Multiply both sides by +B+-+4+
+P+-+120+=+-80%2A%28+B+-+4+%29+
+P+=+-80B+%2B+320+%2B+120+
+P+=+-80P+%2B+440+
check:
Does it include the given points?
(3,200)
+P+=+-80P+%2B+440+
+200+=+-80%2A3+%2B+440+
+200+=+-240+%2B+440+
+200+=+200+
(4,120)
+120+=+-80%2A4+%2B+440+
+120+=+-320+%2B+440+
+120+=+120+
OK

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Suppose you have a cookie stand, and when you charge $3 per cookie box you sell 200 boxes. But when you raise your price to $4 you only sell 120 boxes.
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You have two points: (3,200) and (4,120)
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a. Write an equation for the number of boxes you sell as a function of the price you charge.
slope = (200-120)/(3-4) = -80
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Form: # of boxes = mp + b
Solve for 200 = -80*3 + b
b = 440
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Equation:
# of boxes = -80(charge) + 440
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b. Denote "B" for number of boxes, and "P" for the price you charge.
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c. Assume the function is linear..
B = -80*P + 440
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Cheers,
Stan H.
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