I am trying to help some adults who have not practiced mental arithmetic for decades, but now they have a need for various reasons. I have noticed that they are considerably uneven: $2\times4$, $6\times6$, and $8\times8$ are no problem normally, but for some reason, they are often slow and/or unsure of, for instance, $7\times8$, $3\times9$, $7\times12$, etc.
Are there any known apps or web sites where you can define the multiplications for a certain pupil you observed being slow or unsure? I mean, where you can pick out or choose a specific set of calculations, like "flash cards" and the set time limits for practice of speed and accuracy?
For the purpose we use IPad, and Windows 8 on PC.