TITLE: Cards game and probabilities
QUESTION [10 upvotes]: From a standard 52-cards deck we randomly pull out 2 cards.
  One is black and the other is a 4.
  We choose one of the two cards.
  What is the probability:

The card we pick is a 4
The card we pick is black
The card we pick is a face card


For 1: I believe it must be 1/2 (since 1 of the 2 cards is a 4) plus the probability for the other card also to be a 4. Since the other card is black, we know there are 2 fours in 26 black cards so 2/26? So finally $1/2+2/26$? Not sure.

Similarly, 1/2 + the probability for the "4" card to be black - it can't be $1/2+2/4$ though.
The black card can be a face card with probability $6/26$.

Can you help me out?

REPLY [2 votes]: 1) The card we pick is 4:
How many permutations (ordered pairs) satisfying the criteria (one is 4, the other is black) do we have? We can divde them into two distinct groups:
First group: one card is a black card that is not 4, the other card is 4. There are 24 black cards that are not 4 and each one can be combined with four different 4s. There are $24\times4=96$ ordered pairs starting with a black card that is not 4 and 96 ordered pairs starting with 4.
Second group: one card is a black 4 and the other card is any other 4. Basically, all ordered pairs of 4s are valid (and we have $4\times3=12$ of them) except 2 ordered pairs of red 4s. The total number of odrered pairs satisfying the criteria for the second group is $12-2=10$
So in total we have $2\times96+10=202$ ordered pairs. There are 96 ordered pairs from the first group starting with 4 and 10 ordered pairs also starting with 4. All ordered pairs are equally possible so the probability that your first card is 4 is:
$$\frac{96+10}{2\times96+10}=\frac{106}{202}=\frac{53}{101}\approx0.524752$$
I did a Monte Carlo simulation with 20.000.000+ draws satisfying the conditions of the problem and got 0.524895 which is within 0.03% from the calculated value. The value $\frac{11}{21}\approx0.523810$ obtained by @drhab is obviously not a better match.
2) The card we pick is black:
Again, we have two groups of ordered pairs and we already calculated that the total number is 202.
First group: one card is a black card that is not 4 (24 possibilities), the other card is 4 (4 possibilities, 2 of them black). How many ordered pairs start with a black card? There are $24\times4=96$ ordered pairs starting with a black card that is not 4, plus $2\times24=48$ ordered pairs starting with a black 4. In total, we have $96+48=144$ ordered pairs starting with a black card.
Second group: one card is a black 4, the other card is any other 4. How many ordered pairs start with a black card? There are two black fours and the second card can be any of the remaining three. So in total there are $2\times3=6$ ordered pairs starting with a black card. 
Taking both groups into the account there are $144+6=150$ ordered pairs starting with a black card, so the probability is:
$$\frac{150}{202}=\frac{75}{101}\approx0.742574$$
I did a Monte Carlo simulation with 25.000.000+ draws satisfying the conditions of the problem and got 0.74254516. 
3) The card we pick is a face card:
This is the easiest case.
First group: one card is a black card that is not 4 (24 possibilities), the other card is 4 (4 possibilities, 2 of them black). There are 6 black face cards (J,Q,K) so in total we have $6\times4=24$ ordered pairs starting with a face card.
Second group: one card is a black 4, the other card is any other 4. You cannot pick a face card from any ordered pair belonging to this group.
Taking both groups into account, you have only $24$ ordered pairs starting with a face card so the probability is:
$$\frac{24}{202}=\frac{12}{101}\approx0.118881$$
I did a Monte Carlo simulation with 10.000.000+ draws satisfying the conditions of the problem and got 0.11883492.
If you are interested in Monte Carlo, here is the Java code that I used:
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

class Card {
    public int suite; // 0,1 => black, 2,3 => red
    public int value; // from 2 to 14

    public Card(int suite, int value) {
        super();
        this.suite = suite;
        this.value = value;
    }

    public boolean isFour() {
        return value == 4;
    }

    public boolean isBlack() {
        return suite < 2;
    }

    public boolean isFaceCard() {
        return value >= 12 && value <= 14;
    }
}

class Deck {
    private List<Card> cards = new ArrayList<>();
    private Card c1, c2;

    public Deck() {
        for(int value = 2; value <= 14; value++) {
            for(int suite = 0; suite <= 3; suite++) {
                cards.add(new Card(suite, value));
            }
        } 
    }

    public void drawOneBlackAndOneFour() {
        Random rnd = new Random();
        Collections.shuffle(cards, rnd);
        while(true) {
            int i = rnd.nextInt(52);
            c1 = cards.get(i); 
            while(true) {
                int j = rnd.nextInt(52);
                if(i != j) {
                    c2 = cards.get(j);
                    break;
                }
            }
            if(c1.isBlack() && c2.isFour()) {
                break;
            }
            if(c2.isBlack() && c1.isFour()) {
                break;
            }
        }
    }

    public boolean isFirstCardFour() {
        return c1.isFour();
    }

    public boolean isFirstCardBlack() {
        return c1.isBlack();
    }

    public boolean isFirstCardFaceCard() {
        return c1.isFaceCard(); 
    }
}

public class Test {
    public static void main(String[] args) {
        Deck deck = new Deck();
        int ok = 0, total = 0;
        while(true) {
            total++;
            deck.drawOneBlackAndOneFour();
            if(deck.isFirstCardBlack()) {
                ok++;
            }
            System.out.println(String.format("%d/%d = %.8f", ok, total, (double)ok/(double)total)); 
        }
    }
}