I wanted to have a link in the post, but apparently i can't (for at least three more posts...). So i tried to to the best i could, which is to tell you about the website (5min dot com), and to search it for "learn for the gmat".
I've found it while googling for one of the questions in th OG12
, and saw the given way for that problem. it helped me a lot so far (even though some of the questions are note the same, thus i think it's an older version).