Pete makes house calls to give away free books to families with children. He gives away books to those families that open the door for him when he rings their doorbell and have children living at home. He gives exactly one book to a qualified family. Studies indicate that the probability that the door is opened when Pete rings the doorbell is 0.75, and the probability that a family has children living at home is 0.5. If the events "door opened" and "family has children" are independent, determine the following:
a. The probability that Pete gives away his first book at the third house he visits
b. The probability that he gives away his second book to the fifth family he visits
c. The conditional probability that he gives away the fifth book to the eleventh family he visits, given that he has given away exactly four books to the first eight families he visited.
d. Given that he did not give away the second book at the second house, what is the probability that he will give it out at the fifth house?