The probability of getting a second red card is 25 in 51, or 0.490, because one red card is missing, and the deck is short by one card.
The probability of getting a black card next is 26 in 50, or 0.52, because the deck is short by two cards, but all the black cards are there.
Multiply these probabilities together, and you get about 0.127, or about 1 in 8, so the probability of getting 2 red cards and then a black card in a random 52 card deck is about 1 in 8.