A survey of 21 business intelligence analysts, who had been in their current positions from 10 to

Question:

A survey of 21 business intelligence analysts, who had been in their current positions from 10 to 20 years, revealed $90,734 as the average salary.14 Assume a random sample with a standard deviation of $15,000.
a. Find the 95% confidence interval for the population mean salary.
b. Find the 99% confidence interval for the population mean salary.
c. Complete the following sentence: We are 95% sure that the population mean salary is at least ______________________.