Probabilities Concerning 3-Letter Sequences

1)We construct a 3-letter sequence by randomly choosing the letters A and B with probabilities 2/3 and 1/3 ,respectively

a)What is the probability that we get one of ABB or ABA?

b)What is the probability that the second letter is B?

c)Suppose we win as many TL's as the number of A 's in the word (i.e 1 TL if there is one A, 2 TL if 2 A's, 3 TL if 3 A's).What is the expectation of the money we win?

d)What is the expected number of A's in the word?

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