Math 101
posted by Ann .
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..

Look at it as if you are given two ordered pairs
(3,250) and (4,120) of the form (P,B)
slope = (12025)/(43) = 130/1 = 130
then just like in y = mx + b
B = 130P + b
sub in (4,120)
120 = 130(4) + b
b = 640
B = 130P + 640
check:
if P= 3 , B = 130(3) + 640 = 250
if P = 4 , B = 130(4) + 640 = 120
All is good.