# The Deck of cards!

A standard deck of cards has 26 red cards and 26 black cards. 2 cards are drawn out of the deck. What is the probability the second card is red, given the first card was black (The first card was not replaced in the deck before the second card was drawn.)

$P(R_2 | B_1) = \frac {P(R_2 \cap B_1)}{P(B_1)}$ Does this help?
After drawing the first card, there are 26 red cards and 25 black cards left. You will get a red one with probability $$\frac{26}{25+26}$$