A 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 80% confidence interval for the population mean is 2-A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22, and a standard deviation of 3.6. The 95% confidence interval for the population mean is 3-A random sample of 64 students at a university showed an average age of 20 years and a sample standard deviation of 4 years. The 95% confidence interval for the true average age of all students in the university is