a. A random sample of 11 observations was taken from

a. A random sample of 11 observations was taken from a normal population. The sample mean and standard deviation are x? = 74.5 and s = 9. Can we infer at the 5% significance level that the population mean is greater than 70?,b. Repeat part (a) assuming that you know that the population standard deviation is ? = 90.,c. Explain why the conclusions produced in parts (a) and (b) differ.