## Odds of winning at casino

**Gambling mathematics**November 5, 2015 – 03:12 pm

The mathematics of gambling are a collection of probability applications encountered in games of chance and can be included in game theory. From a mathematical point of view, the games of chance are experiments generating various types of aleatory events, the probability of which can be calculated by using the properties of probability on a finite space of events.

### Experiments, events, probability spaces[edit]

- Throwing the dice in craps is an experiment that generates events such as occurrences of certain numbers on the dice, obtaining a certain sum of the shown numbers, and obtaining numbers with certain properties (less than a specific number, higher than a specific number, even, uneven, and so on). The sample space of such an experiment is {1, 2, 3, 4, 5, 6} for rolling one die or {(1, 1), (1, 2)..., (1, 6), (2, 1), (2, 2)..., (2, 6)..., (6, 1), (6, 2)..., (6, 6)} for rolling two dice. The latter is a set of ordered pairs and counts 6 x 6 = 36 elements. The events can be identified with sets, namely parts of the sample space. For example, the event occurrence of an even number is represented by the following set in the experiment of rolling one die: {2, 4, 6}.

- Spinning the roulette wheel is an experiment whose generated events could be the occurrence of a certain number, of a certain color or a certain property of the numbers (low, high, even, uneven, from a certain row or column, and so on). The sample space of the experiment involving spinning the roulette wheel is the set of numbers the roulette holds: {1, 2, 3..., 36, 0, 00} for the American roulette, or {1, 2, 3..., 36, 0} for the European. The event occurrence of a red number is represented by the set {1, 3, 5, 7, 9, 12, 14, 16, 18, 19, 21, 23, 25, 27, 30, 32, 34, 36}. These are the numbers inscribed in red on the roulette wheel and table.

- Dealing cards in blackjack is an experiment that generates events such as the occurrence of a certain card or value as the first card dealt, obtaining a certain total of points from the first two cards dealt, exceeding 21 points from the first three cards dealt, and so on. In card games we encounter many types of experiments and categories of events. Each type of experiment has its own sample space. For example, the experiment of dealing the first card to the first player has as its sample space the set of all 52 cards (or 104, if played with two decks). The experiment of dealing the second card to the first player has as its sample space the set of all 52 cards (or 104), less the first card dealt. The experiment of dealing the first two cards to the first player has as its sample space a set of ordered pairs, namely all the 2-size arrangements of cards from the 52 (or 104). In a game with one player, the event the player is dealt a card of 10 points as the first dealt card is represented by the set of cards {10♠, 10♣, 10♥, 10♦, J♠, J♣, J♥, J♦, Q♠, Q♣, Q♥, Q♦, K♠, K♣, K♥, K♦}. The event the player is dealt a total of five points from the first two dealt cards is represented by the set of 2-size combinations of card values {(A, 4), (2, 3)}, which in fact counts 4 x 4 + 4 x 4 = 32 combinations of cards (as value and symbol).

- In 6/49 lottery, the experiment of drawing six numbers from the 49 generate events such as drawing six specific numbers, drawing five numbers from six specific numbers, drawing four numbers from six specific numbers, drawing at least one number from a certain group of numbers, etc. The sample space here is the set of all 6-size combinations of numbers from the 49.

- In draw poker, the experiment of dealing the initial five card hands generates events such as dealing at least one certain card to a specific player, dealing a pair to at least two players, dealing four identical symbols to at least one player, and so on. The sample space in this case is the set of all 5-card combinations from the 52 (or the deck used).

- Dealing two cards to a player who has discarded two cards is another experiment whose sample space is now the set of all 2-card combinations from the 52, less the cards seen by the observer who solves the probability problem. For example, if you are in play in the above situation and want to figure out some odds regarding your hand, the sample space you should consider is the set of all 2-card combinations from the 52, less the three cards you hold and less the two cards you discarded. This sample space counts the 2-size combinations from 47.

### The probability model[edit]

A probability model starts from an experiment and a mathematical structure attached to that experiment, namely the space (field) of events. The event is the main unit probability theory works on. In gambling, there are many categories of events, all of which can be textually predefined. In the previous examples of gambling experiments we saw some of the events that experiments generate. They are a minute part of all possible events, which in fact is the set of all parts of the sample space.

For a specific game, the various types of events can be:

- Events related to your own play or to opponents’ play;
- Events related to one person’s play or to several persons’ play;
- Immediate events or long-shot events.

Each category can be further divided into several other subcategories, depending on the game referred to. These events can be literally defined, but it must be done very carefully when framing a probability problem. From a mathematical point of view, the events are nothing more than subsets and the space of events is a Boolean algebra. Among these events, we find elementary and compound events, exclusive and nonexclusive events, and independent and non-independent events.

In the experiment of rolling a die:

- Event {3, 5} (whose literal definition is occurrence of 3 or 5) is compound because {3, 5}= {3} U {5};
- Events {1}, {2}, {3}, {4}, {5}, {6} are elementary;
- Events {3, 5} and {4} are incompatible or exclusive because their intersection is empty; that is, they cannot occur simultaneously;
- Events {1, 2, 5} and {2, 5} are nonexclusive, because their intersection is not empty;
- In the experiment of rolling two dice one after another, the events obtaining 3 on the first die and obtaining 5 on the second die are independent because the occurrence of the second event is not influenced by the occurrence of the first, and vice versa.

In the experiment of dealing the pocket cards in Texas Hold’em Poker:

- The event of dealing (3♣, 3♦) to a player is an elementary event;
- The event of dealing two 3’s to a player is compound because is the union of events (3♣, 3♠), (3♣, 3♥), (3♣, 3♦), (3♠, 3♥), (3♠, 3♦) and (3♥, 3♦);
- The events player 1 is dealt a pair of kings and player 2 is dealt a pair of kings are nonexclusive (they can both occur);
- The events player 1 is dealt two connectors of hearts higher than J and player 2 is dealt two connectors of hearts higher than J are exclusive (only one can occur);
- The events player 1 is dealt (7, K) and player 2 is dealt (4, Q) are non-independent (the occurrence of the second depends on the occurrence of the first, while the same deck is in use).

**Source:** en.wikipedia.org

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The odds are approximately even for every hand you play. Over time though, the house gets a theoretical edge as all bets are taken.

The difference between actual odds and payoff odds is this:

Actual odds are the odds of winning

Payoff odds are how much the casino pays on your bet if you win

Example: Roulette - Actual odds of hitting 18 are 38:1 (36 numbers on the board, plus 0 and 00), Payoff odds are 35:1.

If the actual and payoff odds are 17:15, think of it like this: $17 paid for $15 bet...and you want to know x paid for $13 bet, right?

17 ... x

---- = ---

15 ... 13

(you may know what to do from here)

multiply both sides by 13 to get x alone on one side

17 (13) . x (13)

---- --- = --- ---

15 (1) . 13 …

Actual odds are the odds of winning

Payoff odds are how much the casino pays on your bet if you win

Example: Roulette - Actual odds of hitting 18 are 38:1 (36 numbers on the board, plus 0 and 00), Payoff odds are 35:1.

If the actual and payoff odds are 17:15, think of it like this: $17 paid for $15 bet...and you want to know x paid for $13 bet, right?

17 ... x

---- = ---

15 ... 13

(you may know what to do from here)

multiply both sides by 13 to get x alone on one side

17 (13) . x (13)

---- --- = --- ---

15 (1) . 13 (1)

221 = x

----

15

divide 221 by 15 to equal x

I'll let…

Actual odds are the odds of winning

Payoff odds are how much the casino pays on your bet if you win

Example: Roulette - Actual odds of hitting 18 are 38:1 (36 numbers on the board, plus 0 and 00), Payoff odds are 35:1.

If the actual and payoff odds are 17:15, think of it like this: $17 paid for $15 bet...and you want to know x paid for $13 bet, right?

17 ... x

---- = ---

15 ... 13

(you may know what to do from here)

multiply both sides by 13 to get x alone on one side

17 (13) . x (13)

---- --- = --- ---

15 (1) . 13 (1)

221 = x

----

15

divide 221 by 15 to equal x

I'll let…