@ ElAzar
Hab mich nicht alles durchgelesen, aber einiges und was ich bisher las, kam auch in der Quelle dazu, dass unter den Standard-Festlegungen, die hier gemacht wurden, 2/3 rauskommen.
The behavior of the host is key to the 2/3 solution. Ambiguities in the "Parade" version do not explicitly define the protocol of the host. However, Marilyn vos Savant's solution (vos Savant 1990a) printed alongside Whitaker's question implies and both Selvin (1975a) and vos Savant (1991a) explicitly define the role of the host as follows:
- The host must always open a door that was not picked by the contestant (Mueser and Granberg 1999).
- The host must always open a door to reveal a goat and never the car.
- The host must always offer the chance to switch between the originally chosen door and the remaining closed door.
When any of these assumptions is varied, it can change the probability of winning by switching doors as detailed in the section below. It is also typically presumed that the car is initially hidden behind a random door and that, if the player initially picks the car, then the host's choice of which goat-hiding door to open is random. (Krauss and Wang, 2003:9) Some authors, independently or inclusively, assume that the player's initial choice is random as well. Selvin (1975a)
Wenn die verändert werden, verändert sich die Wahrscheinlichkeit. Aber davon sprach zumindest ich nie, sondern genau das ist mein Bezugsrahmen.
A simple way to demonstrate that a switching strategy really does win two out of three times with the standard assumptions is to simulate the game with playing cards (Gardner 1959b; vos Savant 1996, p. 8). Three cards from an ordinary deck are used to represent the three doors; one 'special' card represents the door with the car and two other cards represent the goat doors.
The simulation can be repeated several times to simulate multiple rounds of the game. The player picks one of the three cards, then, looking at the remaining two cards the 'host' discards a goat card. If the card remaining in the host's hand is the car card, this is recorded as a switching win; if the host is holding a goat card, the round is recorded as a staying win. As this experiment is repeated over several rounds, the observed win rate for each strategy is likely to approximate its theoretical win probability.
Repeated plays also make it clearer why switching is the better strategy. After the player picks his card, it is already determined whether switching will win the round for the player. If this is not convincing, the simulation can be done with the entire deck. (Gardner 1959b; Adams 1990). In this variant, the car card goes to the host 51 times out of 52, and stays with the host no matter how many non-car cards are discarded.