To start this problem you'll find it useful to draw a tree similar to the one in the picture. Your probabilities will differ from those shown in the picture.
Five percent of the people in a certain city are in a high risk group for HIV infection, and 7% of the people in this high risk group are HIV positive. However, only 0.4% of the people who are not in the high risk group are HIV positive. (Hint: Pay special attention when converting percentages into a decimals in this problem.)
Answer the following questions. (Give your answers correct to five decimal places.)
(a) What is the probability that a randomly chosen person from this city is HIV positive?
(b) What is the probability that a randomly chosen person from this city is both in the high risk group AND is HIV positive?
(c) What is the probability that a randomly chosen person from this city is in the high risk group OR is HIV positive OR is both?
(d) If you know that a specific person is HIV positive, what is the conditional probability that this person is in the high risk group?