Good brain trainer app for improving your working memory.
＜ USAGE ＞
1. Select level (1-10).
2. Memorize the answer of easy addition for the level times.
3. Continue memorizing and tap the last digit of the answer of n times before (NOT current answer).
If you don't know what is N-Back, please see below.
http://en.wikipedia.org/wiki/N-back
