Points: 0 of 1 O A random sample of n measurements was selected from a population with unknown mean u and standard deviation o - 35 for each of the situations in parts a ue through d. Calculate a 90% confidence interval for u for each of these situations. a. n= 75, x = 39 ed b. n = 250, x = 111 c. n = 100, x = 13 d. n = 100, x = 5.86 e. Is the assumption that the underlying population of measurements is normally distributed necessary to ensure the validity of the confidence intervals in parts a through d? Explain. a. (Round to two decimal places as needed.)