Codes Memory Test BQ IP

[Black]

Next month I'm going for Lufthansa City BQ through IP as ready entry.
I'm working on the Skytest, but on the memory exercises I can't get a decent score.
I found the Codes Memory Test the most difficult, and I can't get above 45% with medium level.
Does any of you have any trick to improve?
Another difficult question: does any of you have any idea on what's the pass mark? I mean, for other exercises like orientation, multitasking etc, it's probably around 80%, but for memory, I don't think there're many people out there able to reach such a score, so the pass mark must be less