Dear
Danzig,
I would say, when you are doing that well, you are in a region of the CAT where it will throw everything including the kitchen sink at you. To score that high, you have to be nailing almost everything, and when you are performing that well, the CAT will start reaching for the hardest questions in the bank (which is probably why you saw some repeats in your second take). Naturally, the hardest questions are ones that tend to disorient folks a bit and make them feel uncomfortable. Think about those question ---- you felt uncomfortable, so wouldn't it be fair to say that most GMAT test takers would feel uncomfortable on them and probably wouldn't be successful with them? That would place them among the hardest questions, and that's precisely what the CAT will give you when you are getting virtually everything else right.
In some ways, what you are asking is tautological --- why do the hardest questions seem hard? If you are committed to getting an elite Quant score, then by that very fact and by the way the CAT functions, you are committing yourself to face some of the mind-shatteringly difficult questions the folks at GMAC have ever conceived, questions that, at least initially, anyone who doesn't happen to be as bright as Isaac Newton will find puzzling. Of course some of these questions make you uncomfortable!!! How focused and clear-sighted can you remain even when you feel uncomfortable, even when initially you don't know how to approach the problem ---- that's precisely what separates truly extraordinary Quant performances from merely very good performances.
Now, as far as where to find questions such as those, that's a very good question. These blog starts out with some reasonably difficult questions:
https://magoosh.com/gmat/2012/gmat-factorials/https://magoosh.com/gmat/2013/geometric- ... -the-gmat/https://magoosh.com/gmat/2012/gmat-math- ... binations/The NOVA book, while lacking in any substantial explanations, does have some truly difficult practice problems.
To some extent, though, practice problems are missing the point. One of the chief factors that makes a math problem truly hard, 800+ level, is if it is so out-of-the-box that no one approaching it has every seen anything like it before. Any problem that has a recognizable form, something that folks can practice, will necessarily be at least slightly easier than a question of a format that no one has ever seen. Once again, if you are committed to scoring in the elite region on the Quant, then by that very fact, you are committed to seeing some problems that are just completely out-of-left-field, unlike anything in any GMAT practice book on the face of the Earth. A good mathematical problem solver is not phased by this ---- a good mathematical problem-solver can approach a problem she has never seen before, dissect it from fundamental math principles, and solve it. That's what you have to be able to do if you want an elite Quant score.
The most I can say it --- post some of those questions here, and ask the experts: not so much the answer, but tell me how you would think about the problem? what would be your instincts in approaching such a problem? At this level, it's not so much about material or practicing patterns --- it about how to dissect something you have never seen before.
Does all this make sense?
Mike
_________________
Mike McGarry
Magoosh Test PrepEducation is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)