posted by Mike .
A 95% confidence interval for a population mean, ?, is given as (18.985, 21.015). This confidence interval is based on a simple random sample of 36 observations. Calculate the sample mean, x ?, and the sample standard deviation, s. Assume that all assumptions and conditions necessary for inference are satisfied.
95% confidence is two standard deviations about the mean.
Add 18.985 and 21.015 together, then divide by 2. This will be your mean.
Subtract 18.985 from the mean, then divide that result by 2. This will be your standard deviation.