Monty Hall Simulation
Welcome to Code Review and coding in general:


Code according to PEP8 – In your case this means using snake_case for variable and function names, add spaces after commas and between operators. Your code does look rather nice in general, some minor nitpicks here and there, but read through the guidelines and try to adhere to them.
Feature: incorrect_possibilities = possible_answers invalidates possible_answers – When you later on do incorrect_possiblities.remove(correct_answer) this also changes possible_answers. To get a copy you need either to use a better variant of copy, or simply incorrect_possibilities = possible_answers[:]. The latter one uses slicing to denote the entire array, and makes a copy of the sliced area.
Use ternary related to chosen_strategy - Based on the chosen strategy you choose either of two choices, this can be coded as final_answer = correct_answer if chosen_strategy == 1 else your_answer, and similar in the other cases.
Use ternary related to print output also – This can also be used in print out as well:

print("Which means it is either your answer: {}, or the only other remaining option, {}.".format(
      correct_answer if your_answer == correct_answer else  your_answer,
      other_remaining if your_answer == correct_answer else correct_answer))

Use the newer print('You chose {}'.format(final_answer) syntax – This is the preferred version for new code in Python 2 and for code in Python 3. See Format specification mini language for examples and specification.
Use docstrings, """ ... """, and not comments, # ..., when describing modules, functions, classes and methods. – If you use docstrings they can be used by your IDE or documentation tools, and it is according to the Pythonic way. :-)
Avoid one-time temporary variables – The playagain can be dropped if you use while True: to keep the game going, and change the end to something like if int(raw_input("Play again (0 = no)?")) == 0: break. (Preferrably with a newline before the break, which does break out of the while loop)
Possibly add a loop or validation on the main loop – If you enter something when choosing between playing one game at a time, or play a chosen number of games, you can enter something wrong and the script terminates. This could possibly be enhanced by adding a while loop around it.

Do also note that if you enter non-numeric text your code breaks very easily...  Look into making a general int input function which uses try ... except around the input function.
Introducing the if __name__ == '__main__': idiom – The previous code is often used to make the code reusable as a module, and to have as little code as possible at the top level. Combined with a main() function your code easily be reused and extended.

In your case you could use (possibly extended with the while loop):

def main(): 
    game_choice = int(raw_input("Play one game at a time (1) or play your chosen number of games with one strategy (2)? &gt; "))
    play_chosen_game(game_choice)

if __name__ == '__main__':
    break

Consider shortening the text length – Your texts are rather worthy, and could benefit from being shortened a little.


Conclusion

Your code does look good for a beginner, and naming is good (with the exception of not using underscores in between words). You could benefit from learning to use the ternary operator (a if b else c), and a slight justification on using functions related to top level code and text lengths.