A player plays the following game with a casino: a coin is tossed until a tail appears. The player wins 2N dollars where N is the number of heads before a tail appears. If there are no heads, the player wins 20 = $1. The player needs to pay a fee to enter the game and, therefore, in order for the player to decide whether or not the game is worth playing, it is important that the player knows the expected (average) payoff.

The probability that the sequence of events will be N heads, tail (2N payoff) is: (see possible answers below)