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4 Exercise 8-31 Algo The monthly closing stock prices (rounded to the nearest dollar) for Panera Bread Co. for the first six months of 2010 are reported in points the following table. [You may find it useful to reference the t table.] Months Closing Stock Price 110 Book January February 115 March 114 April 113 May 119 Hint June 118 References Source: http://finance.yahoo.com. a. Calculate the sample mean and the sample standard deviation. (Round intermediate calculations to at least 4 decimal places and "Sample mean" and "Sample standard deviation" to 2 decimal places.) Sample mean Sample standard deviation b. Calculate the 90% confidence interval for the mean stock price of Panera Bread Co., assuming that the stock price is normally distributed. (Round ":" value to 3 decimal places and final answers to 2 decimal places.) Confidence interval to c. What happens to the margin of error if a higher confidence level is used for the interval estimate? The margin of error increases as the confidence level increases. O The margin of error decreases as the confidence level increases