FYI - I wasn't able to find your app on my nexus when searching for "math machine". I found it only when looked for "woodencloset".
As for the app - great idea and nice implementation, but for someone who understands what to do right from the beginning, "hints"-popups are really annoying. Maybe add a button "I know what I'm doing" or something like that to allow to skip them?
That's a good idea. I'll think where I can add this without having people press it by mistake and getting lost. About the search, that's an unfortunate part of the play store discovery problem. They prioritize ratings/downloads over keywords...
