Not bad, but I've got some remarks that could make it even better:
1. I barely noticed a difference between the levels of difficulty, maybe only a bit in the case of the "extension" level;
2. Many times you get the same question during one game, once I even got the same question twice in a row;
3. Maybe it would be good to add even harder multiplications like with two two-digit numbers or even three-digit numbers (yes, it is possible to do this just in mind without writing it :-) )
4. If one or more multiplyings are wrong there should be a summary presenting the errors, because while trying to get the best score you don't have the time to check the answer below;
5. According to the scores: maybe a highscore list? :-)
6. I noticed that instead of clicking on the numbers by mouse I can simply write the numbers, but two things need improvements:
a) while writing, it should be like this: you want to write 33 for example, so you should press 3 twice instead of holding the 3 button. Why? Because the game is at the moment too sensitive to writing and for example when I wanted to write 12 it gave me 112 or even 111;
b) the usage of backspace and enter should be enabled, it would make the game much easier to deal with.
Keep it up and it can be really a good thing! :-)