Individuals A and B begin to play a sequence of chess games. Let , and suppose that outcomes of successive games are independent with and (they never draw). They will play until one of them wins ten games. Let of games played (with possible values 10, 11, . . . , 19).

a. For , obtain an expression for

.

b. If a draw is possible, with , ,

, what are the possible values of X? What is ? [Hint:

.]