Q.4 a) Let X follows a Gamma diatribution f(x)=(a)ba,xa1eab,x0,a>0,b>0 Obtain mean, variance of the above distribution. b) Suppose that an average of 15 customers per hour arrive at a shop in accordance with a Poisson process. That is, if a minute is our unit, then =3/4. What is the probability that the shopkeeper will wait more than 5 minutes before both of the first two customers arrive