A random sample of 12 graduates of a certain secretarial school typed an average of 78.9 words per minute with a standard deviation of 7.5 words per minute. Assuming a normal distribution for the number of words typed per minute, find a 99% confidence interval for the average number of words typed by all graduates of this school. Click here to view page 1 of the standard normal distribution table Click here to view page 2 of the standard normal distribution table Click here to view page 1 of the table of critical values of the t-distribution. Click here to view page 2 of the table of critical values of the t-distribution. The confidence interval is