A quality of life survey was conducted with employees of a manufacturing firm. Of the firm's 3000 employees, a sample of 300 were sent questionnaires. Two hundred usable questionnaires were obtained for a response rate of 67%.

a. The mean annual salary for the sample was  = $23,200 with s = $3000. Develop an approximate 95% confidence interval for the mean annual salary of the population.

b. Use the information in part (a) to develop an approximate 95% confidence interval for the total salary of all 3000 employees.

c. Seventy-three percent of respondents reported that they were "generally satisfied" with their job. Develop an approximate 95% confidence interval for the population proportion.

d. Comment on whether you think the results in part (c) might be biased. Would your opinion change if you knew the respondents were guaranteed anonymity?