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From a sample of 41 orders for an on-line bookseller, the average order size is $75, and the sample standard deviation is $18. Assume the distribution of orders is normal. For which interval can one be exactly 90% confident that the population mean is contained in that interval? A. $71.29 to 78.71. B. $74.24 to $75.76. C. $70.27 to $79.73. |