You get 10 points for a correct answer but lose 20 for an incorrect choice.
In addition, you lose a second for every wrong answer in the level so far. So the first mistake costs you one second,
the next two, the third a further three seconds, and so on.
You get points for the time remaining at the end of each level. There may be several identical answers available -
you can pick which of these to use.
There are nine levels, which work through basic addition and subtraction, multiplication, fractions (this is hard),
precidence of the basic operations, powers and finally, all of these together.
You can now submit your score to a high-score table to compare it against the rest of the internet.