random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 3.6. The 90% confidence interval for the population mean is a. 19.62 to 20.38 b. 19.51 to 20.49 c. 19.41 to 20.59 d. 19.30 to 20.70
