4. 20 students were asked how many units they were taking at a community college 5 5 5 8 9 10 10 13 15 15 15 15 15 16 18 19 20 21 22 24 a. Calculate the sample mean. This is a point estimator for the population mean, u. Explain what this means. b. Find a 95% confidence interval for the population mean, assuming o = 5. Calculate and explain the margin of error c. Find a 99% confidence interval for the population mean, assuming o =5. Interpret the interval and explain why the margin or error for the 99% confidence interval is wider than the 95% confidence interval calculated in question 2. 5. Microwave Ovens: In a random sample of 5 microwave ovens, the mean repair cost was $75.00 and the sample standard deviation was $12.50. Assume the random variable is normally distributed and use a t- distribution to construct a 95% confidence interval for the population mean J. What is the margin of error of the confidence interval