A Marketing Research firm was hired to estimate the mean prime-lending rate for banks located in the western region of the United States. A random sample of n = 50 banks was selected from within the region, and the prime-rate was recorded for each. The mean and standard deviation of the 50 prime rates were: mean = 9.1% and std = .24% . If the research firm wanted to be 90% confident in its estimates (z value for 90 percent = 1.645), what would be the confident interval for the estimated mean.
Please give the break-down on how to solve.