Concentration (game) as an educational game. Any deck of playing cards may be used, although there are also commercial sets of cards with images. The rules given here are for a standard deck of 52 cards, which are normally laid face down in four rows of 13 cards each. The two jokers may be included for a total of six rows of nine cards each. Additional packs can be used for added interest. Standard rules need not be followed: the cards can be spread out anywhere, such as all around a room. In turn, each player chooses two cards and turns them
Joker (playing card) cards provide symbols for three jokers: red, black, and white. Many decks do not provide the Joker with a corner index symbol, of those that do, the most common is a solid five-pointed star or a star within a circle. It is also very common for decks to simply use a stylized "J" or the word "JOKER" in the corner. Like sports trading cards, jokers are often prized by collectors. Many unusual jokers are available for purchase online while other collectible jokers are catalogued online for viewing. Some European games have as many as six jokers per pack. Zwicker uses