Question 1192845
you did it right.
it is very possible to get z-score that are very high or very low.
this is one example of that.
it can get even higher than that.
assuming the average time was 30 minutes with a standard deviation of 1 minute and a sample size of 21, then the z-score could have been (30 - 15) / (1/sqrt(21)) = 68.7...
it all depends on what the actual wait time was versus what the claimed wait time was.