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STA 2023, Spring 2005, Quiz 9 Name: ________________________ Instructor: ___________________ Code: _________________________ Round all answers to three decimal places unless otherwise indicated. 1. A 90% confidence interval is to be determined for a population mean based on a sample of size 25, with the population standard deviation unknown. What is the appropriate critical value t α/2? ____1.711_________ A simple random sample of 25 actuaries is selected, and a WAIS-III IQ test is administered to each. The sample mean IQ score is 120. Assume that scores on this IQ test for actuaries are normally distributed, and have a population standard deviation of 15 points. 2. Compute the standard error of the sample mean. _____3________ 3. Determine a 95% confidence interval for the population mean. Express as an interval, with an upper and a lower bound. __(112.12, 125.88)___ 4. For a 95% confidence interval for the population mean were to have a margin of error of exactly 2 IQ points, what sample size would be needed? (round appropriately) _____217________ For a simple random sample of 25 adult males, the sample mean systolic blood pressure (SBP) is 120, with a sample standard deviation of 12. Assume that the SBP of adult males follows a normal distribution. 5. What is the margin of error for a 95% confidence interval for the population mean SBP? ____4.9536_________ 6. What is a 95% confidence interval for the population mean SBP? __(115.0464, 125.9536)_