Chatting Math Drill

"Chatting Math Drill" is voice-only math training drill of 2 digit addition/subtraction.
According with recent neuroscience paper, repeating mental arithmetic enables to strength brain function and to prevent brain from dementia.
And mental arithmetic is also effective for increasing power of concentration and endurance.
Furthermore, with voice-only application, it is possible to do mental arithmetic and body exercise　simultaneously, which is said to be more effective for preventing brain from dementia.