9.4

. A simple random sample of size n is drawn from a population that is known to be normally distributed. The sample variance, s, is determined to be 13. Complete parts (a) through (c). (a) Construct a 90% confidence interval for of if the sample size, n, is 20. The lower bound is (Round to two decimal places as needed.) The upper bound is (Round to two decimal places as needed.) (b) Construct a 90% confidence interval for of if the sample size, n, is 30. The lower bound is (Round to two decimal places as needed.) The upper bound is (Round to two decimal places as needed.) How does increasing the sample size affect the width of the interval? O The width decreases O The width does not change O The width increases (c) Construct a 98% confidence interval for of if the sample size, n, is 20. The lower bound is (Round to two decimal places as needed.) The upper bound is (Round to two decimal places as needed.) Compare the results with those obtained in part (a). How does increasing the level of confidence affect the confidence interval? O The width does not change O The width increases O The width decreases