There are several questions, and please help explain the answer.

1. A fair coin is tossed 10 times. What is the probability of observing a sequence H,H,H,H,H,T,T,T,T,T, and the probability that the sequence will contain 5 heads and 5 tails?
2. A biased coin is tossed 10 times. The coin is biased in a way making it twice as likely to land on the head. What is the probability that the sequence will contain 5 heads and 5 tails?
3. Your team has designed a model to assign a binary sentiment (+or-) marker to a sentence. There are two versions of the model which is model A and model A. Currently, both versions are in production, and traffic is split equally and randomly between two models. Version A is older and has a 75% chance of producing the correct result while Version B is newer and has a 90% chance of producing the correct result. Looking over the system logging file you notices that one of the models incorrectly predicted the sentiment of one sentence. Compute the probability that the sentence in question was graded by model A.