1. A coin is tossed three times. What is the probability that the outcome contains no heads, given that exactly one of the coins shows a tail?
2. Bag of Marbles A bag contains five red marbles and seven white marbles. If a sample of four marbles contains at least one white marble, what is the probability that all the marbles in the sample are white?
3. Balls in an Urn Two balls are selected at random from an urn containing two white balls and three red balls. What is the conditional probability that both balls are white, given that at least one of them is white?