Hi. Welcome to GMAT Club.
The score you get depends on where are you start and how much you improve. Obviously, some starting positions are easier to improve than others and some people start a lot higher another is a lot lower, but On average,
Manhattan GMAT course results into about 120 points of improvement. So if you started at 550 (which by the way is about 50th percentile on the GMAT) with the average amount of effort, you should’ve scored 670.
Putting in additional effort such as chasing every question you get wrong and making sure you address your weaknesses, you can improve about 200 points. It is rather hard to improve more than 200 points though you don’t need to go there. Actually, you didn’t really mention what score you were looking for.
Have you worked on the questions in the official guide? I assume so since the books used to depend on those questions but asking just in case since you didn’t reference them.
It is hard to judge performance based on the number of right or wrong answers. You can definitely miss a third of the questions and still get a good score but the sequence of those mistakes matters a lot. Obviously GMAT is an adaptive test and it changes the question difficulty as you progress and if you make a bunch of mistakes upfront, you’ll never dig out from the hole. If you were curious about number of mistakes you can make, we’ve read a whole bunch of experiments and GMAT prep software but I honestly wouldn’t worry too much about that one.
I am rambling here a little but, in general the score depends on how much you know the material, your ability to follow strategies, and timing. You have to balance the three and they have to work together to result in to the best score doing just one, is not optimal.
If you’re looking to bump up your score which your post sounds like that, your croissant is where you need to put most of your effort. I would say 80% of your effort should go onto Quant since most business calls or skeptical about applicants with Quant below 44 or 45. Your Q 40 indicates some discomfort with math. It seems you can get some quick wins there within a few weeks...
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