Explain probability using multinomial distribution.
A college student is taking five courses in a semester. He is willing to presume that he will get an A with probability 0.1 a B with probability 0.8 and a C with probability 0.1 in each of the courses. He describes X1, X2 and X3 to be the number of A's, B's and C's correspondingly that he gets in the semester. For this multinomial variable situation find-
1) Explain the probability that the student gets all B's.
2) Explain the probability that the student gets 2 A's and 3 B's in the semester.
3) Explain the probability that he gets no C's in the semester.