Determine Probability using multinomial distribution.
A college student is taking 5 courses in a semester. He is willing to assume that he will get an A with probability 0.10, a B with probability 0.80, and a C with probability 0.1 in each of the courses. He defines X1, X2, and X3 to be the number of A's, B's and C's respectively that he gets in the semester. For this multinomial variable situation, find:
a) The probability that the student gets all B's.
b) The probability that the student gets 2 A's and 3 B's in the semester.
c) The probability that he gets no C's in the semester.