Each player has several strategies. If the first player chooses Strategy i while the second player chooses Strategy j, then Player 1 gains while Player 2 gains . This outcome is represented by . 2-person games where the players' interests are completely opposed are called zero-sum or constant-sum games: one player's gain is the other player's loss. Games where the players' interests are not completely opposed are called variable-sum games. Such games arise in business on an everyday basis, and solving them is not an easy task. Certain 2-person games admit pure strategies whereas others require mixed strategies. A pure strategy is one where, each time the players play the game, they choose the same strategy. A mixed strategy is one where the players introduce a random element in their choice of a strategy, thus leaving the opponent guessing.