A social service agency plans to conduct a survey to determine the mean income of its clients. The director of the agency prefers that you measure the mean income very accurately, to within plus or minus $500. From a sample taken two years ago, you estimate that the standard deviation of income for this populatation is about $5,000. You job is to figure out the necessary sample size to reduce sampling error to plus or minus $500.
a. do you need to have an estimate of the current mean income to answer this question? why or why not?