9.8 An efficiency expert wishes to determine the av- erage time that it takes to drill three holes in a certain metal clamp. How large a sample will she need to be 95% confident that her sample mean...

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Extracted text: 9.8 An efficiency expert wishes to determine the av- erage time that it takes to drill three holes in a certain metal clamp. How large a sample will she need to be 95% confident that her sample mean will be within 15 seconds of the true mean? Assume that it is known from previous studies that o = 40 seconds.