14-8. Because of the current concern over credit card balances, a bank's chief nancial ofcer is interested in whether there is a relationship between account balances and the number of times a card is used each month. A random sample of 50 accounts was selected. The account balance and the number of charges during the past month were the two variables recorded. The con'elaon coefcient for the two variables was 0.23. a. Discuss what the r = CL23 measures. Make sure to frame your discussion in terms of the two variables mentioned here. b. Using an a: = 0.10 level, test to determine whether there is a signicant linear relationship between account balance and the number of card uses during the past month. State the null and alternative hypotheses and show the decision rule. c. Consider the decision you reached in part b. Describe the type of error you could have made in the context of this problem. 14-10. Amazon.com has become one of the most successful online merchants. Two measures of its success are sales and net income/loss figures (all figures in $million). These values for the years 1995-2007 are shown as follows. Year Net Income/Loss Sales 1995 -0.3 0.5 1996 -5.7 15.7 1997 -27.5 147.7 1998 -124.5 609.8 1999 -719.9 1,639.8 2000 -1,411.2 2,761.9 2001 -567.3 3,122.9 2002 149.1 3,933 2003 35.3 5,263.7 2004 588.5 6,921 2005 359 8,490 2006 190 10,711 2007 476 14,835 a. Produce a scatter plot for Amazon's net income/ loss and sales figures for the period 1995 to 2007. Does there appear to be a linear relationship between these two variables? Explain your response. b. Calculate the correlation coefficient between Amazon's net income/loss and sales figures for the period 1995 to 2007. c. Conduct a hypothesis test to determine if a positive correlation exists between Amazon's net income/ loss and sales figures. Use a significance level of 0.05 and assume that these figures form a random sample.14-50. A statistics student was recently working on a class project that required hint to compute a correlation coefficient for two variables. After careful work, he arrived at a correlation coefcient of 0.45; Interpret this correlation coecient for the student who did the calculations