7. The classification of stochastic models according to: discrete or continuous time variable with discrete or continuous state space gives rise to a four-way classification. Give four practical problems, one of each type, of stochastic models which may be used to model observed processes. 8. Find the generating function for the given sequences i) ii) {0,1,4,9,...) {0,1,8,27,....} iii) (1.4.9) iv) (1.8,27,...) 9. Determine the probability generating function and hence mean and variance of the following a) Poisson b) Geometric c) Negative binomial 10. Let X be a discrete random variable with PGF P(s) = (2+3s). Find the distribution of X S 5