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Question 993687: The manager at a local Best Buy store kept track of daily sales of the iPhone 6 when it was first introduced. He noticed that sales were very high at first, but showed a steady decrease. For example, on day 5 after the phones first went on sale, the store sold 238 iPhone 6’s, but on day 10 after the phones first went on sale, the store sold only 153 iPhone 6’s. Assume that the relationship between number of days since the phone became available and number sold is linear and, let x = the number of days since the phone was released and y = number of phones sold at this Best Buy store.
a) Write two ordered pairs to represent the sales on the days described.
b) Find the slope of the line through those ordered pairs.
c) Write an equation in point-slope form of the line.
y
d) Convert the equation to slope-intercept form.
e) Explain what the slope and the y-intercept mean in the context of this problem.
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! (5,238)
(10,153)
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slope is (153-238)/(10-5)= -85/5 = -17
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y-y1= -17(x-x1). use either ordered pair. This is the point slope approach.
y-238= -17(x-5));;point slope formula
y-238= -17x+85
y= -17x+323 slope-intercept form.
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Slope of -17 means that every day, 17 fewer iPhones are being sold.
Intercept of 0 means that on the first day 323 were sold. Often, y-intercepts are not helpful but may be useful here.
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