In: Statistics and Probability
Let N be the number of requests to a web server per day and let N Poisson(). Each request
comes from a human with probability p or from a spam bot with probability 1 ? p. Assume that
the requests are independent of each other. Let X be the number of requests from humans per
day and Y be the number of requests from spam bots per day.
(a) State the conditional distribution of X given N = n, and state the conditional distribution of
Y given N = n.
(b) Calculate the probability of getting exactly x human requests and y spam requests.
(c) Find the joint probability mass function of X and Y , and show that X and Y are independent
of each other.
(d) Using your result in part (c), compute E[X + Y ] and Var[X + Y ].