from a standard pack of 52 cards, you and your friend are getting 7 cards each, given the fact that you have 4 hearts, whats the probability that your friend has 3 hearts.
at first i marked the event $A$ as the event of you get 4 hearts and the event $B$ of your friend getting 3 hearts. so we are looking for $\mathbb{P}[B|A]$.
so from the formula of conditional probability we need $\mathbb{P}[B\cap A]$ and $\mathbb{P}[A]$
$\mathbb{P}[A]$ we can get by: $$\frac{\binom{13}{4}}{\binom{52}{7}}$$ but when im trying to find $\mathbb{P}[B\cap A]$ im running to troubles.