I think a couple of things need to be clarified here:

Rich said:

The scores that matter are the SCALED SCORES, which tell you how you performed relative to the Test. These are the numbers that go into calculating your GMAT score.

Actually this is not correct. Both your scaled scores and your overall 200-800 scores are based on your "raw score" - which is essentially your percentile (the GMAT uses the term "theta" but it works just like a percentile). The way that the test is scored is that the test calculates your "theta" (compared to tens of thousands of people who have taken the GMAT) THEN the test givers you an overall score and the scaled scores based on that raw score / theta.

Please read this statement from GMAC "Your total score is based on raw performance on both the Verbal and Quantitative sections. A range of raw scores will map onto a single scaled score, but since the Total score is based on the raw performance, greater differentiation is possible."

Rich also said:

Percentiles are often mis-understood pieces of information (and can also be deceptive). A percentile lets you know how you performed relative to OTHER Test Takers, NOT how well you performed relative to the Test.

The Official GMAT test evolves based on ACTUAL student responses. The difficulty level is EXPLICITLY a comparison to other test takers - as indeed it must be.

The flaw that is committed by many unofficial practice tests (I am not sure how the one that you took is scored but it may contain this flaw as well) is that the test writers decide how hard they think that a particular question is and they continue to assign that level of difficulty to that same question year after year.

This is what is great about the new Veritas Practice tests. Like the official GMAT they evolve based on actual student responses during the test. 1.5 million student responses up to this point

So take the FREE Official GMATPrep Test or take the Veritas FREE Practice Test to see how you score.

Now, to more explicitly answer your question victor_vdpc -

Scoring is not based only on how many questions you got right and but on the difficulty level of those questions. The test is adapting to you so that you are constantly facing questions that should challenge you.

I can see why you would have some confusion given that on the actual GMAT (or GMATPrep official practice test) 12 questions wrong on the Quant section is nearly guaranteed to be over the 50th percentile and usually higher than that. Whereas you missed only 10 questions and earned a 45th percentile.

As Rich said different practice tests are scored different ways. I do not know much about this particular test but I would encourage you to take one of the tests I mentioned above, the Veritas test or the GMATPrep to get a better idea of where you stand.

Finally, here is a link to an article written by Brian Galvin Vice President of Academic Programs at Veritas. This article explains the GMAT scoring system in great detail! https://poetsandquants.com/2013/07/21/th ... t-scoring/