Lee agreed to use "MathTango" everyday 

Lee likes this game and trained himself at the same time to be good at math.

For many weeks he chose to do the same lesson over and over again. Robin was amazed to watch how he built a strong formation for calculation in his brain. He did it over and over again. And it was very easy. 

The repetition of something easy is very beneficial when it is enjoyed. Robin is doing it for himself. As long he enjoys something easy, he will keep doing it over and over again. No need to move on to something more difficult.

But one day Lee decided to move on and learn different math. He was going through it with an immense speed.