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

In poker, players form sets of five playing cards, called hands, according to the rules of the game. Each hand has a rank, which is compared against the ranks of other hands participating in the showdown to decide who wins the pot. The number of different 5 -card poker hands is. 52 C 5 = 2,598,960. A wonderful exercise involves having students verify probabilities that appear in books relating to gambling. For instance, in Probabilities in Everyday Life, by John D. McGervey, one finds many interesting tables containing probabilities for poker and other games of chance.

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.

Poker Hand Scenarios Games

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.

Poker Hand Scenarios Meaning

Definitions of Poker Hands

Poker Hand Scenarios Vs

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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.

Poker Hand Scenarios Free

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 Hand Scenarios Against

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2017 – Dan Ma

What does Computer Hand mean in Texas Hold'em? This is a nickname for being dealt the Queen-Seven offsuit hand in the hole. Your two cards would be a queen and seven with suits that don't match. This is regarded as not being a good starting hand because your odds of winning with it are almost exactly even.

Why Is Queen-Seven Offsuit Called the Computer Hand?

There are two theories, but one has the benefit of being shown to match the odds of winning with the Q-7 offsuit hand. Years ago (no date is given) someone ran all the possible combinations of Texas Hold'em starting hands through a computer simulator, and it was found that in random hands, Q-7 won roughly 50 percent of the time and lost 50 percent of the time. It's considered the 'median' starting hand.

Run through various poker simulators, the Q-7 offsuit hand is shown to win 51.766 percent in a showdown against random hands in Texas Hold'em poker. This places it exactly in the middle of starting hand combinations. If you're dealt a Q-7 offsuit and play it through to the showdown, your odds are just about even of winning the hand.

With a Q-7 offsuit, you have a chance of pairing the queen, which is a decent hand unless a king or ace is revealed on the board. But you also have the risk that another player is holding a queen and has a better hole card than the seven. You will have to use your skills to read the board and read the other players to determine whether to hold them or fold them. Of course, you could catch a great flop leading to three of a kind, full house, or four of a kind.

Best and Worst Starting Hands in Texas Hold'em Poker

Poker Hand Scenarios Without

The five best starting hands in Texas Hold'em poker are pairs of aces, kings, queens, jacks, and the ace-king combination. Those are hands with the best odds of winning if played to the showdown. The worst starting hands include the dreaded 7-2 offsuit combination, with suited 7-2 being only slightly better. What makes this hand so bad is that you can't make a straight with it and both are low cards that would make low pairs. A flush with suited 7-2 would be low and easily beaten by another player holding the same suit.

Poker Hand Scenarios

Apocryphal Story of the Computer Hand

Other stories as to why the Q-7 is called the computer hand are that the odds were run with only a small sample size and by pure chance, it came out as the most winning hand. This would be due to the inherent sampling error seen when you use a small sample size. Odds are determined by running very large sample sizes with correctly-written algorithms. It is easy to see unusual patterns if you don't run through enough scenarios, or if the program introduces its own biases. However, any player may decide that this combination is their lucky one and play it accordingly.