Question: Thirty percent of credit card holders carry no monthly balance, while 70% do. Of those card holders carrying a balance, 30% have annual income $20,000 or less, 40% between $20,001 and $50,000, and 30% over $50,000. Of those card holders carrying no balance, 20%, 30%, and 50% have annual incomes in these three respective categories.
(a) What is the probability that a randomly chosen card holder has annual income $20,000 or less?
(b) If this card holder has an annual income that is $20,000 or less, what is the probability that (s)he carries a balance?