To calculate the conditional probability \( P(\text{brown} | \text{black}) \), we need to understand what this probability represents. It is the probability of selecting a brown pair of shoes given that we have selected a black pair of shoes.
However, since brown and black pairs are mutually exclusive (you cannot have a shoe that is both brown and black), the probability of selecting a brown pair given that you have a black pair is \( 0 \).
Therefore, we can conclude:
\[ P(\text{brown} | \text{black}) = 0 \]