Mental computation training

I played this game when I'm 11 while study math. My Math teach have 2 class. He play this game with our class, but not with another. It lasts about 9 months, 15 minutes game time every day. 9 years later， there are 5 students get into college，I'm one of five， only one in another class， Since I'm in a very low education quality middle school. For some unknown reason it works. I don't know why, Just write it, hope it can help you. Rules. 1. 999 levels. 2. Game start, it will show you card one by one，if it's red one("Heart", "Diamond"), You should add this number but if it's black one("Spade", "Club") You should minus its value."J" is 11."Q" is 12,"K" is 13. For example: Heart 3, Spade 5, Club Q, Diamond 9, Result should be -5, you need input -5 to pass this level.