In continuation to my post above, I would like to tell here that I agree with 90% of the things mentioned here. I am in complete agreement with the statements below –
a) Official questions are of the best quality, closest to the actual questions and most dependable practice material
b) You should practice official questions more than any other unofficial questions
c) Some of the questions of the big test prep companies are too difficult or too easy or ambiguous or not related to GMAT concepts
I even agree with the below statement but with a caveat.
d) You can score a 700+ or even a 780 by practicing / studying only official guides, questions and tests without touching any other unofficial source at all and without help from any test prep company’s material / course.
The caveat for statement d is that you need to learn the concepts of GMAT from a very good GMAT tutor who can guide you how to use the official materials and questions. This caveat is never mentioned in any of the posts here as that will look like a direct advertising and people may not take it as a neutral advice.
You can score a 700+ without knowing anything about probability. I was weak in probability and I am not sure whether I gave correct answer to the only probability question in my actual GMAT or not. I scored 760. But along with probability if you are unsure about number properties, word problems, inequality, geometry and co-ordinates and have a speed problem in RC and not confident in answering difficult RC and SC questions then you cannot score 700+ even if you practice 4000+ official questions over 3-4 months.
Unless you are already strong with most of the GMAT concept (which is only true for probably less than 5% of the candidates), you need to build the concepts tested in GMAT to score 700+. It’s ok if you are weak in 3-4 specific topics like probability, co-ordinates, bold face CR, idioms etc, but then you need to be confident in other areas.
You can build the concepts in three ways –
Option 1) Taking help from a test prep company,
Option 2) Taking help from a good GMAT tutor and
Option 3) For self prep, use unofficial guides like
MGMAT SC and quants guide or
PowerScore CR Bible and associated topic wise unofficial questions. Use some official questions in between for practice.
After you build the concepts in the first 20% or 30% part of your preparation, you can devote the last 70-80% part to official questions. If you are targeting a 700+ score by self prep only not taking any help from a big test prep company or a GMAT tutor and you are only using official materials / questions / tests avoiding all unofficial materials then you are putting yourself into a big risk of not achieving your target score.
Again, I am not a GMAT tutor or expert, but I have seen people practicing only a lot of official questions without building the concepts well with help from any GMAT tutor or unofficial materials and failing to achieve their target score. They are inspired by the advices like a, b, c above but did not understand the caveat in statement d as it is not explicitly mentioned.
Sorry for the long post again, but in summary, my advice is if you are only practicing official questions, go for option 2 above, otherwise go for option 1 or 3.