154 CHAPTER 3
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a. The trend line estimates that the price was $432 in
November 2007 and $80 in September 2011. (That is an
interval of 46 months.) Use this information to determine
the slope of the trend line. Round your answer in dollars
per month to two decimal places. Be careful about the sign.
b. Use your answer to part a to determine by how much
the price of a Kindle should decrease every six months.
c. Use the information in part a to find a formula for the
price, in dollars, as a linear function of the time in months
since November 2007.
d. Use your answer to part c to determine the prediction
of the trend line for the price in July 2012 (56 months
after November 2007). What do you conclude from this
unreasonable result?
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