Integer division?

There is no decimal point. Integer division can be useful, but not when trying to learn basic math. Also, "teens and adults" would probably need to practice things like x^2-4x+4=0, or d/dt(-9.81t^2). This app only does the four basic functions, which literally any calculator can do for you.
Additionally, quick inputs are impossible. Try typing 11 at a reasonable speed and you get 1.

Yankeexpress about Math Duel: Equation Practice