12.82 Lexus, Inc. The Lexus GX is a mid- size sport utility vehicle (SUV) sold in North American and Eurasian markets. The GX 470 was introduced in 2002 (as a 2003 model) and was later upgraded with a new off-road suspension system. The sales of the Lexus GX 470 from its inception until 2009 are given in the table:

a. Plot the data using a scatterplot. How would you describe the relationship between year and sales of the Lexus GX 470?

b. Even though the scatterplot in part a might indicate differently, assume that the relationship between year and sales is linear. Find the least-squares regression line relating the sales of the Lexus GX 470 to the year being measured.

c. Is there sufficient evidence to indicate that sales are linearly related to year? Use a = 0.05.

d. Examine the diagnostic plots shown below. What can you conclude about the validity of the regression assumptions?

e. Based on your conclusions in part

d, is it advisable to predict the 2010 sales using the regression line from part b? Explain.

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Calendar Year Total Sales (U.S.) 2002 2,190 2003 31,376 2004 35,420 2005 34,339 2006 25,454 2007 23,035 2008 15,759 2009 6,235