GREAT MATH APPS!
Math Bingo for iPhone, iPod touch, and iPad on the iTunes App Store
https://itunes.apple.com/us/app/math-bingo/id371338715?mt=8

Math Ninja HD for iPhone, iPod touch, and iPad on the iTunes App ... https://itunes.apple.com/us/app/math-ninja-hd/id370144476?mt=8

Repeated subtraction using the "Chunking" method
http://www.chunkydivision.co.uk/activity/index.htm