An economist is interested in studying the monthly income of people in a particular city. Assume that income is normally distributed. Based on prior research, the population standard deviation is known to be $2,000. A random sample of 80 individuals resulted in a mean income of $18,000. The economist wants to estimate the 95% confidence interval.

(a) What is the margin of error of the confidence interval?

(b) What is the width of the confidence interval?

(c) What is the upper confidence limit of the confidence interval?

(d) What is the lower confidence limit of the confidence interval?

Now consider that instead of 95% confidence level, we are considering 99% confidence level. The economist wants to find the margin of error.

(e) What is the Excel formula to compute the answer?