Math Gym creates puzzles designed to exercise your mental arithmetic.

A series of calculations scroll up the page, and you have to work out the final answer. As you progress, the math gets harder and scrolls away faster, but you can always pause it and even ask for help if needed.

With 10 levels of difficulty (from simple addition and subtraction through to cube roots and primes), and 10 speed settings, there is something to challenge everyone from elementary school to math graduate.

The screenshots show sample puzzles at levels 3 and 8 (on a scale from 1 to 10). Note that the harder puzzles are designed so that it often helps to look at several steps together.