The average time interval between successive barges passing a certain point on a busy waterway is 10 minutes.

a. What is the probability that exactly 7 barges pass the certain point with one minute interval? (Here the number of passing barges is a discrete random variable]

b. What is the probability that at least 3 barges pass the certain point with one minute interval?

C. Find the probability that the time interval between two successive barges is between 1/80 minutes and 1/40 minutes