Question: Question 21

A consumer group wants to estimate the mean electric bill for the month of July for single-family homes in a large city. Based on studies conducted in other cities, the standard deviation is assumed to be $25. The group wants to estimate the mean bill for July within ± $5 of the true average with 99% confidence.

a. What sample size is needed?

b. If 95% confidence is desired, what sample size is necessary?

c. If you want to be 95% confident of estimating the population mean to within a sampling error of ± 5, and the standard deviation is assumed to be equal to 15, what sample size is required?