There are two main modes (Singleplayer and Multiplayer)

In singleplayer mode you can improve your mental arithmetic skill and compare your skill with others or just train your simple math skills.
This app provieds three types of complexity (Easy,Average,I am genius) and for each type a set of exercise types.
Exercise types: Division, Addition, Subtraction, Multiplication, Mixed,Square Root (√x),Squaring (x²),Cubing (x³), Fraction Addition, Fraction Subtraction, Fraction Multiplication, Fraction Division, Fraction Mixed, Linear Eqations, Next Prime, Complex and much more.
It includes a Highscore for each complexity and exercise type. This Highscore is available online: http://mentalarithmetic.ctvnet.ch/
After a competition you can see your results to determine what was correct and what was wrong.
In the training mode you can set a custom number range for your questions.
the app supports App2sd for android 2.2 and greater.

In multiplayer mode you can challenge your friends directly!
You have to play 6 rounds alternately. The player who has more correct answers will win the game.
The time to answere is limited and it's multiple choice
There is a online ranking (http://mentalarithmetic.ctvnet.ch/ranking/) players who win a lot earns points, players who loose a lot looses points. players who give up loose automatically and loose points

Thank you for your feedback! We give our best to improve the app depending on your feedback.
Have fun!