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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?
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. 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)
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
5. What is the margin of error for a 95% confidence interval for the population mean SBP?
6. What is a 95% confidence interval for the population mean SBP?
__(115.0464, 125.9536)_