Combination Formula. The Combination of 4 objects taken 3 at a time are the same as the number of subgroups of 3 objects taken from 4 objects. Take another example, given three fruits; say an apple, an orange, and a pear, three combinations of two can be drawn from this set: an apple and a pear; an apple and an orange; or a pear and an orange. Poker Maths - Combinations What is Poker Combinatorics? Combinatorics is the practice of breaking down ranges and counting individual combinations of hands. One of the most popular poker games is 7-card stud. The way hands are ranked is to choose the highest ranked 5-card hand contained amongst the 7 cards. People frequently encounter difficulty in counting 7-card hands because a given set of 7 cards may contain several different types of 5-card hands. Most poker games are based on 5-card poker hands so the ranking of these hands is crucial. There can be some interesting situations arising when the game involves choosing 5 cards from 6 or more cards, but in this case we are counting 5-card hands based on holding only 5 cards. The total number of 5-card poker hands is.

If you were to shuffle a deck of 52 cards and lay them out the possible order combinations are practically endless. The total number of combinations is a factorial of 52, or 52!, which translates to 8.06e+67, a number that means absolutely nothing to me. I probably haven’t thought about Factorials in Math since college. The last class/time I can remember having to use them was in Econometrics. That class was miserable, and the only good thing to come out of it was the teacher convinced me to read The Ultimate Hitchhiker’s Guide to the Galaxy by Douglas Adams. This isn’t a boring ass and explanation of factorials like I probably got back in that class, no, this explanation of how many order combinations there are in a 52-card deck of cards just shredded my brain to pieces.

I came across this explanation of how many order combinations there are in a 52-card deck of cards in an AskReddit thread about ‘coolest mathematical facts’, which I thought was an oxymoron until I read this:

I’ve seen a really good explanation of how big 52! actually is.
Set a timer to count down 52! seconds (that’s 8.0658×1067 seconds)
Stand on the equator, and take a step forward every billion years
When you’ve circled the earth once, take a drop of water from the Pacific Ocean, and keep going
When the Pacific Ocean is empty, lay a sheet of paper down, refill the ocean and carry on.
When your stack of paper reaches the sun, take a look at the timer.
The 3 left-most digits won’t have changed. 8.063×1067 seconds left to go. You have to repeat the whole process 1000 times to get 1/3 of the way through that time. 5.385×1067 seconds left to go.
So to kill that time you try something else.
Shuffle a deck of cards, deal yourself 5 cards every billion years
Each time you get a royal flush, buy a lottery ticket
Each time that ticket wins the jackpot, throw a grain of sand in the grand canyon
When the grand canyon’s full, take 1oz of rock off Mount Everest, empty the canyon and carry on.
When Everest has been leveled, check the timer.
There’s barely any change. 5.364×1067 seconds left. You’d have to repeat this process 256 times to have run out the timer. (via techniforus)

Did I just have an LSD flashback because it feels like that’s exactly what just happened while trying to process this information? If that explanation wasn’t crazy enough, check out this quote:

“Any time you pick up a well-shuffled deck, you are almost certainly holding an arrangement of cards that has never before existed and might not exist again.” – Yannay Khaikin…..Why do I feel like I’m suddenly in one of those ‘this is your brain on drugs’ commercials from the 1990’s?

There was some other mind-blowing math facts in that AskReddit thread, and you can read through all of them HERE, but nothing that really fucked with my mind quite like the explanation of how many card combinations there are.

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This post works with 5-card Poker hands drawn from a standard deck of 52 cards. The discussion is mostly mathematical, using the Poker hands to illustrate counting techniques and calculation of probabilities

Working with poker hands is an excellent way to illustrate the counting techniques covered previously in this blog – multiplication principle, permutation and combination (also covered here). There are 2,598,960 many possible 5-card Poker hands. Thus the probability of obtaining any one specific hand is 1 in 2,598,960 (roughly 1 in 2.6 million). The probability of obtaining a given type of hands (e.g. three of a kind) is the number of possible hands for that type over 2,598,960. Thus this is primarily a counting exercise.

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Preliminary Calculation

Usually the order in which the cards are dealt is not important (except in the case of stud poker). Thus the following three examples point to the same poker hand. The only difference is the order in which the cards are dealt.

These are the same hand. Order is not important.

The number of possible 5-card poker hands would then be the same as the number of 5-element subsets of 52 objects. The following is the total number of 5-card poker hands drawn from a standard deck of 52 cards.

The notation is called the binomial coefficient and is pronounced “n choose r”, which is identical to the number of -element subsets of a set with objects. Other notations for are , and . Many calculators have a function for . Of course the calculation can also be done by definition by first calculating factorials.

Thus the probability of obtaining a specific hand (say, 2, 6, 10, K, A, all diamond) would be 1 in 2,598,960. If 5 cards are randomly drawn, what is the probability of getting a 5-card hand consisting of all diamond cards? It is

This is definitely a very rare event (less than 0.05% chance of happening). The numerator 1,287 is the number of hands consisting of all diamond cards, which is obtained by the following calculation.

The reasoning for the above calculation is that to draw a 5-card hand consisting of all diamond, we are drawing 5 cards from the 13 diamond cards and drawing zero cards from the other 39 cards. Since (there is only one way to draw nothing), is the number of hands with all diamonds.

If 5 cards are randomly drawn, what is the probability of getting a 5-card hand consisting of cards in one suit? The probability of getting all 5 cards in another suit (say heart) would also be 1287/2598960. So we have the following derivation.

Thus getting a hand with all cards in one suit is 4 times more likely than getting one with all diamond, but is still a rare event (with about a 0.2% chance of happening). Some of the higher ranked poker hands are in one suit but with additional strict requirements. They will be further discussed below.

Another example. What is the probability of obtaining a hand that has 3 diamonds and 2 hearts? The answer is 22308/2598960 = 0.008583433. The number of “3 diamond, 2 heart” hands is calculated as follows:

One theme that emerges is that the multiplication principle is behind the numerator of a poker hand probability. For example, we can think of the process to get a 5-card hand with 3 diamonds and 2 hearts in three steps. The first is to draw 3 cards from the 13 diamond cards, the second is to draw 2 cards from the 13 heart cards, and the third is to draw zero from the remaining 26 cards. The third step can be omitted since the number of ways of choosing zero is 1. In any case, the number of possible ways to carry out that 2-step (or 3-step) process is to multiply all the possibilities together.

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The Poker Hands

Here’s a ranking chart of the Poker hands.

The chart lists the rankings with an example for each ranking. The examples are a good reminder of the definitions. The highest ranking of them all is the royal flush, which consists of 5 consecutive cards in one suit with the highest card being Ace. There is only one such hand in each suit. Thus the chance for getting a royal flush is 4 in 2,598,960.

Royal flush is a specific example of a straight flush, which consists of 5 consecutive cards in one suit. There are 10 such hands in one suit. So there are 40 hands for straight flush in total. A flush is a hand with 5 cards in the same suit but not in consecutive order (or not in sequence). Thus the requirement for flush is considerably more relaxed than a straight flush. A straight is like a straight flush in that the 5 cards are in sequence but the 5 cards in a straight are not of the same suit. For a more in depth discussion on Poker hands, see the Wikipedia entry on Poker hands.

The counting for some of these hands is done in the next section. The definition of the hands can be inferred from the above chart. For the sake of completeness, the following table lists out the definition.

Definitions of Poker Hands

Poker Hand Combinations Math

Poker Combinations Math Cheat

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Counting Poker Hands

Straight Flush
Counting from A-K-Q-J-10, K-Q-J-10-9, Q-J-10-9-8, …, 6-5-4-3-2 to 5-4-3-2-A, there are 10 hands that are in sequence in a given suit. So there are 40 straight flush hands all together.

Four of a Kind
There is only one way to have a four of a kind for a given rank. The fifth card can be any one of the remaining 48 cards. Thus there are 48 possibilities of a four of a kind in one rank. Thus there are 13 x 48 = 624 many four of a kind in total.

Full House
Let’s fix two ranks, say 2 and 8. How many ways can we have three of 2 and two of 8? We are choosing 3 cards out of the four 2’s and choosing 2 cards out of the four 8’s. That would be = 4 x 6 = 24. But the two ranks can be other ranks too. How many ways can we pick two ranks out of 13? That would be 13 x 12 = 156. So the total number of possibilities for Full House is

Note that the multiplication principle is at work here. When we pick two ranks, the number of ways is 13 x 12 = 156. Why did we not use = 78?

Flush
There are = 1,287 possible hands with all cards in the same suit. Recall that there are only 10 straight flush on a given suit. Thus of all the 5-card hands with all cards in a given suit, there are 1,287-10 = 1,277 hands that are not straight flush. Thus the total number of flush hands is 4 x 1277 = 5,108.

Straight
There are 10 five-consecutive sequences in 13 cards (as shown in the explanation for straight flush in this section). In each such sequence, there are 4 choices for each card (one for each suit). Thus the number of 5-card hands with 5 cards in sequence is . Then we need to subtract the number of straight flushes (40) from this number. Thus the number of straight is 10240 – 10 = 10,200.

Three of a Kind
There are 13 ranks (from A, K, …, to 2). We choose one of them to have 3 cards in that rank and two other ranks to have one card in each of those ranks. The following derivation reflects all the choosing in this process.

Two Pair and One Pair
These two are left as exercises.

High Card
The count is the complement that makes up 2,598,960.

The following table gives the counts of all the poker hands. The probability is the fraction of the 2,598,960 hands that meet the requirement of the type of hands in question. Note that royal flush is not listed. This is because it is included in the count for straight flush. Royal flush is omitted so that he counts add up to 2,598,960.

Probabilities of Poker Hands

Poker Combinations Math Game

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2017 – Dan Ma