STA 409 Lecture Notes - Lecture 3: Box Plot

The queue manager at a bank believes that their clients spend, on average, less than 15 minutes in the queue. To test his belief the manager commissioned a study, which found out that, from a random sample of 80 customers, the average waiting time was 18 minutes. Assume a population standard deviation of 3 minutes and that the waiting time is approximately normally distributed.
(a) Formulate the null and the alternative hypothesis for this test situation. 
(b) Which test statistic (z or t) is appropriate for this test? Give a reason for your answer. 
(c) Conduct a hypothesis test for a single mean at 5% significance level. Interpret your results