I don't know what formula to use to solve this problem. It sounds like a Geometric Distribution but I'm not sure.
After repeated observations, it has been determined that the waiting time at the drive-through window of a local bank is skewed left, with a mean of 3.5 minutes and a standard deviation of 1.9 minutes. A random sample of 100 customers is to be taken. What is the probability that the mean of the sample will exceed 4 minutes?
The answer the teacher provided is 0.0042.