A supermarket claims that the average wait time at the checkout counter is less than 9 minutes. Assume that we know that the standard deviation of...

A supermarket claims that the average wait time at the checkout counter is less than 9 minutes.  Assume that we know that the standard deviation of wait times is 2.5 minutes.

Consider

H0: mu >= 9

H1: mu < 9

A random sample of 50 customers yielded an average wait time of 8.2 minutes.

What is the value of the test statistic (Zstat or z-sub-xbar)?

(Provide two decimal places)