I still cant see why you cant use what Maurits suggested?
You could have say 10 samples per bus stop. So you have ten rows, each row calculating the total travel time for a random number of passengers. Then you could average these time to a mean total travel time.
Then do another 10 rows for the other bustop, and calculate the total times for another 10 random samples.
I dont think you can post images into messages. You could up load your Excel file and post a link here.