Bidding war

Bidding War is a card game typically involving two players. A radical variation of the classic game War, the result is not predetermined and a good player can win consistently.
Since the game does not require cards to be placed on a table, it can be played in a car or even while standing or walking, which makes it popular among travelers.
It uses a standard Anglo-American playing card deck.

The deck is divided evenly between the two players, giving each a face-down stack of 26 cards. Each player peeks at the top card of his/her stack. Similar to Blackjack, cards with a number 2 to 10 printed on them count as that value; the jack, queen, and king (also known as "face cards") count as 10; the ace card counts as 1.
One of the players (player A) declares his/her guess for the sum of 2 top cards (between 2 and 20). Player B declares his/her guess, which must be bigger than the first guess plus one or lesser than the first guess minus one (so if player A guessed 13, Player B can't guess 12, 13 or 14). The cards are exposed and the player closer to the actual sum receives both cards and places them face up at the bottom of his stack (the end of the "Battle").

If a player guessed the sum exactly, he additionally receives the next top card of both stacks and places the 2 cards face up at the bottom as well.

If both players are equally close to the actual sum, a "Bidding War" takes place:
Both players peek at the next 2 cards of their stacks. Player A guesses the sum of all 4 cards. Player B can either guess a higher number or say 'call'. The players alternate, each one can raise the guess or call. Once a call was made, the 4 cards are exposed and the person who called wins all 6 cards if the sum is smaller than the called guess. The other player wins if the sum matches or is higher.
For example - Player A: 18, Player B: 22, Player A: 23, Player B: 24, Player A: Call. Player A wins if the sum is 23 or under and Player B wins if the sum is 24 or higher.

The next battle is played with player B now guessing first.

The game ends after all 26 cards are played. If a Bidding War occurs when there are no more face down cards (or only one), 2 random cards (or one) are chosen from the face up cards that were already played.

Although using the mathematically correct guess increases the chance of getting the 'accurate guess' 2 cards bonus, being consistent is often a bad strategy in the long run. A good player will recognize the pattern and have a huge advantage when guessing second - knowing what his opponent has.
Somewhat similarly to Poker, a player will try to "read" his opponent according to previous battles. This is especially true during a Bidding War, where physical aspects (such as the time each player takes to think about his next move) during the bidding provide additional information (known as tells)

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Wikipedia