2Vaniver6moThat is, where did 8/15 and 9/15 come from?
Let's step through the B case. I only need to track probability of TS, because
probability of PP is 1 minus that. The RD turns into .9/3 = 9/30ths, the R turns
into 6/30ths, and the FS turns into 3/30ths. Add those together and you get
9+6+3=18, and 18/30 simplifies to 9/15ths.
What about the A case? Here the underlying probabilities are 1, .6, and 0, so
10/30, 6/30, and 0/30. 16/30 simplifies to 8/15ths.

Thank you for this article. Can you please guide me on how did you simplify and compute the probability of A & B in the final step.