GMAT is an adaptive test that measures your skill level by throwing 500+, 600+, 700+ questions. How many of such questions would you see in the test depends on your skill level. Typically, the test would start of with couple of 600+ question and if you answer them correctly, the 9 - 10 questions. Later questions would be around your skill level and if you answer all the questions correctly, the questions get tougher and tougher - 700+, 750+.. so, if your skill level is 700+ you might see lot of 700+ questions.
Occasionally, GMAT tricks you and gives you a 600 level while you are at 700+ and if you answer such question wrong, your score will fall drastically and it would be difficult to recover especially at the later end of test.. Hence, while preparing you want to 1st make sure you can answer all easy correctly. Next, make sure all medium questions are answered correctly.. on a consistent manner.. no careless errors.. then move on to tough or 700 level questions..
Remember, if you can't answer easy and medium level questions correctly for whatever reason - test anxiety, lack of sleep the previous night, lack of focus, you'll never see a 700 level questions on the test..
These are takeaways from a 500 scorer looking to improve to 700.
Good luck with your preparations...
//kudos please, if the above explanation is good
KUDOS is a way to say Thank You