Two Question

You may want to look into the Leitner System, which is a popular method of studying with flashcards using spaced repetition. It was developed by the German commentator and author Sebastian Leitner who described it in his best-selling book Learning How To Learn (So lernt man lernen). It can also be found referred to as the Leitner Method, Leitner Principle, Leitner Cardfile System or the Leitner Cardbox System. Spaced repetition makes studying with flashcards much more efficient and effective.

How does it work?

The idea is that the easier it is to recall the material on a flashcard, the less often that flashcard will be repeated in the future. The reverse follows. The harder it is to recall the material on a flashcard the more often it will be repeated. The repetition of each flashcard is scheduled, or spaced, in such a way that the learner spends most of their time studying material that is more challenging. Material that has been retained well is studied only occasionally to ensure it has not been forgotten.

Look up the Leitner method on the internet and I bet you will be pleased with applying its methods to your GMAT study, particularly on the problems you seem to be missing consistently.