Card counting is almost synonymous to black jack casino game. If you know this strategy you can pretty much guess the probability of each cards that will be dealt.
The basic theory of counting cards is determining the likelihood that the next card you will be dealt is the card that you want. This is easy to do if you're playing black jack using just one deck of cards. For example in a regular 52-deck cards, the probability that and Ace will be dealt first is 4 in 52, or one in 13.
Casinos can prevent players from card counting from being effective because they use multiple decks and have a stop point part of the way through the shoe so that they never deal all the cards inside it. Nonetheless, a simple card counting strategy can be followed effectively using the Plus or Minus system. In this card counting system a value is assigned to each card of +1, zero or -1 as follows:
| Cards | Assigned Value |
| 2, 3, 4, 5, 6 | +1 |
| 7, 8, 9 | 0 |
| 10, Jack, Queen, King, Ace | -1 |
As each card is dealt on the table the player keeps a running count, adding 1 if the card is a 2, 3, 4, 5 or 6, and subtracting 1 for each 10-value card or Ace dealt.
However, casinos consider this skill as a way of cheating the house. Although it is very seldom that a player will be caught doing it. A black jack player faces lifetime ban from entering the casino once he's caught card counting.
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