An investment advisor recommends the purchase of stock shares in Infomatics, Inc. He has made the following predictions: P(Stock goes up 20% | Rise in GDP) = .4 P(Stock goes up 20% | Level GDP) = .5 P(Stock goes up 20% | Fall in GDP) = .6 An economist has predicted that the probability of a rise in the GDP is 40%, whereas the probability of a fall in the GDP is 40%. a. What is the probability that the stock will go up 20%? b. We have been informed that the stock has gone up 20%. What is the probability of a rise or level in the GDP?