The Mathematics of Poker

[Pirana]

This book is definitely not for the average poker players, but it is excellent for those who can comprehend it. I noticed an error on the top of page 18:
p(A & B & C) = (11 / 245) * (9 /48)
= 33 / 3920 (not 4020).

I have a question about equation 3.2 on page 36. I don't understand how the numerator "p(A | B) p (B)" was arrived at. Shouldn't the numerator be
p(A) p(B | A)?