Addition Aliens Game - Version 1.0 A great way for kids or adults to improve their addition and subtraction skills. This math game will let you blast through the alien hordes by typing out the sum or difference between the numbers you see above the aliens as they attack. There are four difficulty settings you can play. Beginner, Intermediate, Advanced, and Impossible. The higher difficulties not only have aliens that attack more frequently and move more quickly, but they also require you to add or subtract larger numbers.