The Lexus GX is a midsize sport utility vehicle (SUV) sold in North American and Eurasian markets by Lexus. 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:18

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 = .05.
d. Examine the diagnostic plots shown below. What can you conclude about the validity of the regression assumptions?
Diagnostic plots for Exercise 12.77
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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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Generation Model(s) Calendar Year Total Sales (U.S.) 2002 2003 2004 2005 2006 2007 2008 2009 2,190 31,376 35,420 34,339 25,454 23,035 15,759 6,235 UZJ120 GX 470 Normal Probability Plot (response is Sales) 95++-+-+-+-+-+-+-+-+-+ +--十 80- 一 30 20 -T--ㄏㄧㄧㄏㄧ-1 10 -30000-20000-10000 10000 20000 30000 Residual Versus Fits (response is Sales) 10000 5000- 0 35000 -10000 -15000 20000 -1000 17000 18000 19000 20000 21000 22000 23000 24000 25000 26000 Fitted Value