Players A and B take turns answering trivia questions, with Player A starting the game by attempting to answer the first question. Each time Player A attempts to answer a question, she has a probability PA of getting the answer right, while each time Player B attempts an answer, he has probability pB of getting the answer right. If Player A attempts m answers, and Player B attempts n answers, what is the probability mass function for the total number of questions they answer correctly? (You can leave your answer in the form of a summation!) Describe exactly when/whether this pmf is equivalent to a binomial distribution. (Hint: Vandermonde's identity, m + n might help you here.)