The table below shows the number of cars (in millions) sold in the United States for various years and the percent of those cars manufactured by GM.

Use a statistical software package to answer the following questions.
a. Is the number of cars sold directly or indirectly related to GM’s percentage of the market? Draw a scatter diagram to show your conclusion.
b. Determine the correlation coefficient between the two variables. Interpret the value.
c. Is it reasonable to conclude that there is a negative association between the two variables? Use the .01 significance level.
d. How much of the variation in GM’s market share is accounted for by the variation incars sold?

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Year Cars Sold (millions) 1950 1955 1960 1965 1970 1975 1980 6.0 7.8 7.3 10.3 10.1 10.8 11.5 Percent GM 50.2 50.4 44.0 49.9 39.5 43.1 44.0 Year 1985 1990 1995 2000 2005 2010 Cars Sold (millions) 15.4 13.5 15.5 17.4 16.9 11.6 Percent GM 40.1 36.0 31.7 28.6 26.9 19.1