Put all of the cards in a pile, face down.
Each player chooses a card and solves the addition or subtraction problem.
If there are 2 players: The player with the greater answer wins the round.
If there are more than 2 players: Put the answers in order from least to greatest. The player with the greatest answer wins the round.
Each time you win a round, collect the losing cards from the other players.
The player with the most amount of cards at the end is the winner!