The problem is that people get good at taking the
MGMAT tests but the real GMAT is slightly different and the math isn't usually as convaluted as it is in
MGMAT tests. The trick is to do as many actual gmat problems as you can and to then go over your errors to make sure that you don't make them any more. The difference between the GMAT and
MGMAT exams is something like the difference between playing full court five on five basketball and playing 21 (I'm going to assume that you know what it is... if not you might want to google it). The skills are mostly transferable between both sports but if you train for 5 on five then your solo 21 game will probably be good but not as good as it could be if you had trained for 21 and used 5 on 5 full court as a means to focus on certain skills sometimes.