A player is dealt two cards from a 48-card deck, where half the cards are black and the other half are red. If the first card is not a red card, the player replaces it randomly in the deck before drawing the second card. If the first card is a red card, the player sets it aside and then draws the second card.
If the second card drawn is a red card, what is the probability that the first card drawn was a black card?
The probability is $\boxed{}$
(Type an integer or a fraction. Simplify your answer.)