5. Determine the critical value z_/2 that corresponds to a 82% level of confidence.

6. Determine the critical value z_/2 that corresponds to a 92% level of confidence.

7. A marketing research company needs to estimate which of two medical plans its employees prefer. A random sample of employees produced the following confidence interval for the proportion of employees who prefer plan A: (0.257, 0.557)

Identify the sample proportion and the margin of error for estimating the true proportion of employees who prefer Plan A.

8. A pollster wishes to estimate the number of left-handed scientists. How large a sample is needed in order to be 95% confident that the sample proportion will be within four percentage points of the true proportion? A previous study indicates that the proportion of left-handed scientists is 17%.

Always round up sample size to the next whole number.

9. A researcher at a major clinic wishes to estimate the proportion of the adult population of the United States that has sleep deprivation. How large a sample is needed in order to be 95% confident that the sample proportion will be within 3 percentage points of the true proportion? No previous estimate is available.

Always round up sample size to the next whole number.

10. A doctor at a local hospital is interested in estimating the birth weight of infants. How large a sample must she select if she desires to be 90% confident that her estimate is within 4 ounces of the true mean? Assume that s = 9 ounces based on earlier studies.

Always round up sample size to the next whole number.