Calculating the standard error and size of the margin of error
A random sample of 81 credit sales in a department store showed an average sale of $68.00. From past data, it is known that the standard deviation of the population is $27.00.
a. Determine the standard error of the mean.
b. With a 0.95 probability, what can be said about the size of the margin of error?
c. Illustrate what is the 95% confidence interval of the population mean?