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a) What is the probability that she devotes precisely three hours to each subject?

b) What is the probability that she devotes three hours to one subject, then four hours to two subjects and two hours to two remaining subjects?

So, I mapped it out and for a) got the sequence of PPC PPC PPC PPC PP (P for plain, C for choc candy) and then used the hypergeom form to get (15 choose 2) times (4 choose 1) divided by (19 choose 3) and get 43% but it's only for the first subject, the first PPC. But if I multiply by the rest of the subjects, the numbers are too big.

For the second one, PC PPPC PPPC PC P, and for this one I am not sure if it would also be hypergeom? I also though I could use neg bin by letting X equal the success=chocolate, but the numbers are not working out.

Any help is appreciated!! Thanks!