The proprieter of the IIT 7-Eleven serves an average of 800 students a day, with inter-arrival times following an exponential distribution. Most students check out with very few items, but there are some that do all their grocery shopping there, which results in service times that are non-exponential. Based on recorded data, the checkout clerk takes an average of 1.2 minutes to ring up a student, with a standard deviation of 3.5 minutes.

How many students, on average, are waiting to be checked out?