An engineering professor purchases a new computer every two years

with preferences for the three model: M1, M2, and M3. If the present

model is M1, the next computer may be M2 with probability .2, or M3

with probability 0.15. If present model is M2, the probabilities of

switching to M1 and M3 are 0.6 and 0.25, respectively. And, if the

present model is M3, then the probabilities of switching to M1 and M2

are 0.5 and 0.1, respectively. Represent the situation as a Markov chain

and determine the probability that the professor will purchase the

current model in four years