The listed values are waiting time (minutes) of customers at the Super Dollar Bank, where customers enter a single waiting line that feeds three teller windows.

6.5 6.6 6.7 6.8 7.1

7.3 7.4 7.7 7.7 7.7

a) Use 0.05 significance level to test the claim that the standard deviation of waiting times is less than 1.9 min, which is the standard deviation of waiting times at the same bank when separate waiting lines are used at each teller window.

b) Construct the 95% of the confident interval for the standard deviation.