Vehicles arrive at a road junction at an average of 4 per min.

Assume that the vehicle arrivals are independent random events

and that the probability distribution does not change with time.

a) What is the probability that 1 or more vehicles arrive at the

junction in a 20 s interval?

(10)

b) What is the probability of having to wait less than 2 min for a

vehicle to arrive at the junction?