A sample is selected from one of two populations, S1 and S2, with probabilities P(S1) !.7 and P(S2) !.3. If the sample has been selected from S1, the probability of observing an event A is P(A!S1) !.2. Similarly, if the sample has been selected from S2, the probability of observing A is P(A!S2) !.3. a. If a sample is randomly selected from one of the two populations, what is the probability that event A occurs