You are getting ready to take a sample from a large population, and need to determine the appropriate sample size. You are estimating sales at a large chain of department stores. A previous survey from the same population found a standard deviation of $18. What sample size is needed to have a 95% confidence of estimating the population mean within plus/minus $5? Show your work.

Answer 1

95% = mean ± 1.96 SEm

1.96 SEm = 5

SEm = SD/√n