8. (20 points) Customers are asked to make a determination about their satisfaction following a visit to a convenience store. The following table reports how many new and returning customers are either satisfied or unsatisfied. Satisfied Unsatisfied New 400 200 Returning 500 100 a. If a customer is selected at random, what is the probability of selecting a returning customer? b. If a customer is selected at random, what is the probability of selecting a new customer given the customer is an unsatisfied customer