A psychologist determined that the number of sessions required to obtain the trust of a new patient is either 1, 2, or 3. Let x be a random variable indicating the number of sessions red the patient's trust. The following probability function has been proposed. f(x) = =for x = 1, 2, or 3 == (a) Is this probability function valid? Explain. This probability distribution --Select-- valid because ---Select--- for x = 1, 2, 3. Also, f(x) = [ (b) What is the probability that it takes exactly 2 sessions to gain the patient's trust? (Round your answer to three decimal places.) (c) What is the probability that it takes at least 2 sessions to gain the patient's trust? (Round your answer to three decimal places.)