Monsters Outnumbered

From BoardGameGeek:

Monsters Outnumbered is a math-based card game that uses strategy, deception, and a team of monsters who have taken on number form. Players sabotage each other's Hordes (equations) with calculated assaults while tactically working to strengthen their own. Only the most cunning will be able to command their monsters to victory by achieving the highest Horde in the deadly arena. Players accomplish this using addition, subtraction, multiplication, division, and ability cards. Games can be played in teams or free-for-all. —description from the publisher