Originally posted by: RapidSnail
Didn't read the thread:
P = (4/52) * (3/51) * (2/50) * (1/49)
P = (24/6 497 400)
P = 1/270 725
Dependence(P^2) = (1/270 725)^2
Dependence(P^2) =
1/73 292 025 625
?
Edit: I may have misapplied dependence. Dependence is whether or not one probability affects the probability of another outcome, if I recall correctly. My reasoning is that if the first four-of-a-kind doesn't occur, then the second four-of-a-kind can't occur with regards to the criteria. Or does the criteria not affect the outcome?
Edit 2: I guess my answer only works if after each card is delt, the next is delivered out of random (no linear progression through the stack). I'm not sure how to make it work for traditional poker though.
Not quite the way to work out the probability. The problem is that there are 5 cards in the hand, not 4. Also, you're working more toward the probability of having 4 of a particular rank. Thus, after your first card, which could be *any* card from the deck (you're not limited to just 4), the probability of the second card matching the 1st card is 3/51, then 2/50, and 1/49. But the probability of the 1st card is 52/52. Also note: the probability of the 5th card not matching the first 4 is 48/48.
Unfortunately, this still doesn't lead to the correct probability because no one said you had to be dealt your 4 of a kind on the first 4 cards. The 5th card could have been the 1st, 2nd, 3rd, 4th, or 5th card. Thus, there are 5 different ways to be dealt that hand.
5 * 52/52 * 3/51 * 2/50 * 1/49 * 48/48 = 74880/311,875,200
Usually, people working with probabilities wouldn't prefer to do it this way - it's too easy to make a logical mistake.
The better way to do it is the number of possible 4 of a kind hands divided by the total number of possible hands.
The total number of possible hands is the number of combinations that can be made from 5 cards. 52C5 (or whatever notation you want for combinations) This is 2,598,960 hands
(or 52*51*50*49*48 divided by the number of arrangements of 5 cards: 5*4*3*2*1)
The total number of 5 card hands with 4 of a kind: Choose one rank out of the 13 (i.e. you could have four A's, four 2's, etc.) There are 13 different choices, times 48 other cards remaining. Four 2's and the 3 of clubs, Four 2's and the 3 of spades, Four 2's and the 3 of diamonds, four 2's and the 3 of hearts; four 2's and the 4 of... i.e. 13*48 possible hands.
So, your probability is 13*48 = 624 / 2,598,960
There are quite a few ways to determine the number of 4 of a kind hands.
Since there's 4 of a kind, they'll be of two different ranks. One of the ranks has 4 out of 4 of that rank, the other rank has 1 out of 4.
Choose 2 ranks, choose 4 out of 4 of that rank, choose 1 out of 4 of the other rank (and the tricky part, times 2 because the 4 out of 4 can be either of the two ranks that you select):
13C2 * 4C4 * 4C1 *2 = 624