The number of people visiting a local shop can be modeled by Poisson distributions
with an average of 0.25 person per minute on a weekday, and an average of 0.5 person
per minute during weekend.
a) Compute the probability of having no visitors to the shop for the interval of 2 hours on
Sunday, knowing that parameter  of the Poisson distribution represents the average
number of visitors for the given time interval.
b) For a randomly selected time interval of 20 minutes on a random day it was observed
that there were no visitors to the shop. Compute the probability that this observation was
made on a weekday (i.e. not Saturday or Sunday)