B. One of my friends had four children, each a boy. She had really been hoping for a girl for some time and reasoned that she should try again. After all, having four boys in a row was an unlikely enough event—what were the chances of the even less likely event of five boys in a row?

a. How many possible gender sequences are there for a woman who gives birth to four children?

What does this imply for the probability that the sequence will be “all boy”?