A supermarket claims that the average wait time at the checkout counter is less than 8 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 8 minutes.  Assume that we know that the standard deviation of wait times is 2.5 minutes. We will test at a significance level of 10%.

Consider

H0: mu >= 8

H1: mu < 8

A random sample of 50 customers yielded an average wait time of 7.8 minutes.

What is the critical value for the Zstat (the Z-test statistic)?

(Provide two decimal places)