a. The mean of a random sample of 25 observations

a. The mean of a random sample of 25 observations from a normal population with a standard deviation of 50 is 200. Estimate the population mean with 95% confidence.,b. Repeat part (a) changing the population standard deviation to 25.,c. Repeat part (a) changing the population standard deviation to 10.,d. Describe what happens to the confidence interval estimate when the standard deviation is decreased.