Messages arrive at an interactive message center according to a counting process with the average inter-arrival time of 15 seconds. Choosing a frame size of 5 seconds, compute the probability that during 200 minutes of operation, no more than 750 messages arrive.
so I know: T = 15 seconds = 1/4 minutes delta = 5 seconds = 1/12 minutes t = 200 minutes lambda = 1/15 seconds so need to find P(x<=750)
My question is which formulas should I use?