The number of people arriving for treatment at an emergency room can be modeled by a Poisson process with a mean of 7 people per hour. How many people do you expect to arrive during a 55-minute period?

I Expect 6.4167 persons arriving during a 55.minute period.

Step-by-step explanation:

If the mean in one hour (60 minutes) is 7, then in a 55 minute period you can expect, by using a rule of three, 7*55/60 = 6.4167 persons. This is because the amount of expected people is always proportional to the amount of time spent waiting for poisson distributions.