Chapter 16, Problem 72E

Two teams (call them $X$ and $Y$ ) play against each other in the World Series. (The World Series is a best-of-seven series: The first team to win four games wins the series, and games cannot end in a tie.) We can describe an outcome for the World Series by writing a string of letters that indicate (in order) the winner of each game. For example, the string $XYXXYX$ represents the outcome: $X$ wins game 1, $Y$ wins game 2, $X$ wins game 3, and so on.

a. Describe the event “ $X$ wins in five games.”

b. Describe the event “the series is over in game 5.”

c. Describe the event “the series is over in game 6.”

d. Find the size of the sample space.