A student wanted to construct a 95% confidence interval for the mean age of students in her statistics class. She randomly selected 9 students. Their mean age was 19.1 years, with a sample standard deviation of 1.5 years. What is the 95% confidence interval for the population mean? What is the sample mean? Calculate the standard error? Find the t-value corresponding to a sample size of 9. (Hint: Either use a t-table or Tools -> Statistical Tables in Gretl. The d.f. = 8 and the right-tail probability is 0.025.) Construct the 95% confidence interval for the mean age of the students.