Good question - I think people are often a little bit surprised at the difficulty of the really-tough official test-day problems compared with OG specifically. The truly hard (scaled 49-51) problems in quant are a little scarce in the OG, which has a lot of 75th-80th percentile type questions but maybe only a handful of really hard questions (total estimate on my part but I'll explain a little).
I think a huge factor in that is that you've seen the OG problems, so some of the problems that you would see while scoring 49-51 on the test are, by definition, "new" whereas the OG problems you've done once, looked at again, discussed on BTG, etc. The GMAT makes questions difficult by positioning them in way that you've probably never seen, in which it takes a step or two to bring them into your wheelhouse.
The practice test questions don't get discussed as much because, since it's adaptive, not everyone sees the same questions. And those have the potential to be newer, and the adaptive nature of the test means that it has to have a deeper bank of hard questions to stay true to its mission, so those are a better indicator for you.
If you look at a bell curve, by far most people won't see the 5% hardest questions on the GMAT, so the OG does a great job of showing people what they'll tend to see...its job isn't to prepare anyone to score 750+ but rather to show people what kinds of questions/concepts it tests. So... my advice if you're going to score high:
-Take the OG questions you've seen and ask yourself how to make them harder. Add a step or two, or turn a hard Problem Solving question into a slightly-harder Data Sufficiency question, and by doing so you'll start to anticipate how the test will ask you hard questions. For example, there's that great remainder problem in OG12 to the extent of:
For integers m and n, when m is divided by n, the remainder is 14. And when m is divided by n, the result is 65.4. What is the value of n?
For my really-advanced students, I asked how they could make that a Data Sufficiency problem and make it even harder. As it stands, that PS version is pretty tough...most people miss it. But now that people have seen it and had it explained it may have lost some of its "99th percentile potential" and the GMAT has to find a way to make those harder. So I tweaked it to:
For nonnegative integers x and y, what is the remainder when x is divided by y?
(1) x/y = 13.8
(2) The numbers x and y have a combined total of less than 5 digits
The result is an even-harder version of the original, and by writing something like this I also had to think like the authors. In addition to "people struggle with the concept of remainders", what else could make this problem hard? Well, abstract statements like statement (2) are hard for people to put into practice. And divisibility rules (that the .8 on x/y corresponds to a ratio of 4/5 for remainder-to-y really frustrates people) are also tricky. So by forcing myself to write a question like this I also learned how the GMAT could do it: combine a remainder-themed problem with a ratio theme, make it Data Sufficiency, and you have a really tough problem. So...as a test-taker, now I see that link between division/remainder/ratio, one I might not have seen before if I hadn't tried to make a hard problem even harder.
I hope that explanation helps (and the correct answer is C, by the way) - by forcing myself to think of how a question could be 10-20% harder, I've also figured out at least one way that the GMAT could do it to me, and that adds new knowledge and understanding of "harder problems".
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank.
Learn More.
