13 An analyst takes a random sample of 25 firms in the telec

13. An analyst takes a random sample of 25 firms in the telecommuications industry and constructs a confidence interval for the mean return for the prior year. Holding all else constant, if he increased the sample size to 30 firms, how are the standard error of the mean and the width of the confidence interval affected? A.) Standard error of the mean increases, Width of confidence interval becomes wider. B.) Standard error of the mean increases, width of confidence intervale becomes narrower. C.) Standard error of the mean Decreases, width of confidence interval becomes wider. D.) Standard error of the mean decreases, width of confidence interval becomes narrower. E.) Cannot be determined.

14.) Professors of accountancy are in high demand at American universities. A random sample of 28 new accounting professors found the average salary was $135 thousand with a standard deviation of $16 thousand. Assume the distribution is normally distributed. Construct a 95% confidence interval for the salary of new accounting professors. Give your answers in thousands of dollars.

15.) A marketing firm wants to estimate how much root beer the average teenager drinks per year. A previous study found a standard deviation of 1.12 liters. How many teenagers must the firm interview in order to have a margin of error of at most 0.1 liter when constructing a 99% confidence interval.

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