SubtractionGame.net has free online math and arithmetic games you can play to improve your math skills. The games on this site are great for kids who are just learning, and adults who would like to improve their mental quickness. Each game on this site has four levels of difficulty, Beginner, Intermediate, Advanced, and Impossible. The games are designed to play like arcade shooters, where the player solves math problems to zap aliens that are attacking the city. If the player takes too long to zap the alien, the alien will drop a bomb on the city. If your city is completely destroyed you lose the game. Each alien has a math problem above them. Type the answer to that problem on your keyboard to zap the alien.