I think before you worry about just getting a crapload of tough questions, you should really evaluate why you are having trouble with the ones you have in front of you. The

OG is generally organized in difficulty order, so it is not surprising for anyone to start noticing that both their speed and accuracy begin to dip as they progress through the book. The problem is that just getting a bunch more questions to practice most likely won't fix the underlying problem.

A lot of people can brute force their way through the early questions because they are easier. Meaning they can do them without using the strategies that they have learned in the different course materials that are available. They revert to their basic math that would make their high school teachers proud, but just because you

get a problem correct, doesn't mean you

did the problem correctly. Most GMAT problems allow for a shortcut that you may have missed and when you get to the harder questions, you have reached the limit of your math skills, but those shortcuts would make the problem significantly easier. But if you didn't practice those shortcuts on the early problems you are not likely to implement them on the harder ones.

As a basic example, I often ask my students what is 7 x 4? They quickly respond with 28. I then ask them how they got it. Did they add seven 4s together? That is, afterall, what 7 x 4 means - 4+4+4+4+4+4+4. Maybe they realized order of multiplication doesn't matter, so they added four 7s. 7+7+7+7. That would be faster. Of course, no one did either of these things. Years ago, someone told them for problems like this, it would be faster to have the stuff memorized, and they were able to just spit out the answer - 28. None of these methods is "wrong" in the sense that they will all arrive at the correct answer, but clearly we went from a long way, to a slightly better way, to the best way. This is what I mean by it is possible to get the right answer without doing the problem the right way.

You should therefore, really go back to questions 1-150 and ask yourself could I have done these problems differently? more efficiently? Then you will learn tricks that will help on the harder problems. Getting a stronger foundation will assist your efforts here. If you have any questions, post the

OG# here (don't post the actual question), and I can show you what I mean about some shortcuts. For example, question 189 in OG11, problem solving section). It is not terribly hard to do algebraically, but if you just think of x as 100, you could probably do it in your head without even drawing out a thing. Not to mention, literally finish the questions in 10 seconds. If x is 100 then the problem reads 2 + 4 is what percent of 100. In other words, 6 is what percent of 100. The answer is now obviously 6.