a 8.39 a. A random sample of 400 observations taken from a population produced a sample mean equal to 92.45 and a standard devia- tion equal to 12.20. Make a 98% confidence interval for u. b. Anbther sample of 400 observations taken from the same population produced a sample mean equal to 91.75 and a standard deviation equal to 14.50. Make a 98% confidence interval for . c. A third sample of 400 observations taken from the same population produced a sample mean equal to 89.63 and a standard deviation equal to 13.40. Make a 98% confidence interval for . d. The true population mean for this population is 90.65. Which of the confidence intervals constructed in parts a through c cover this population mean and which do not? K