The GMAT is provided as a computer adaptive test, or CAT, in most countries of the world. This means of course that you take the test on a computer, but more importantly, that the testing software actually adapts to your performance as you progress through the exam. Because of this, you must be aware of the CAT format and how it will affect your performance on the GMAT.
The CAT is more than just a computerized test
With the CAT format, the computer actually adapts to your performance as you progress through the test questions. Therefore, no one in the testing room will actually be given exactly the same test, because each question you are given is chosen by the computer as a direct result of the one you answered previously. Most people will never have taken this kind of exam before, so take some time to learn how the system works. Understanding the CAT and knowing the test-taking strategies appropriate to this particular format can have a direct, positive impact on your score.
How does the CAT work?
When you begin a section on the CAT, the computer assumes you have an average score (~500) and gives you a question of medium difficulty level. If you answer this question correctly you will be given a more difficult question (worth more points); but answer it incorrectly and you will be given an easier question which will have a negative impact on your score.
As it tries to determine your final score, the computer makes larger jumps in difficulty at the beginning of a section to quickly find your approximate scoring level. Then it makes smaller jumps to fine-tune your score. Therefore, you should be aware that the first few questions of each section can make a big impact on your final score, but equally you must know that every single question you answer will affect your score.
No going back to check your answers!
Because each right or wrong answer directly affects the next question the test gives you, the CAT does not allow you to go back to questions you've already answered and double-check your work. The CAT is designed to only shows you one question at a time and does not allow you to see the next question until you've responded to the one at hand. So be as sure as possible that you have answered a question correctly before moving on. Once you've noted and confirmed your answer, that's it - you won't be given a chance to return to it.
Leave no question unanswered
All the above being said, if you are given a question that you cannot answer, you should definitely make a guess. Guess intelligently and strategically rather than at random—try to eliminate any wrong answer choices that you can spot and guess from amongst those remaining.
You will be penalized for every question that you do not answer on the GMAT. If you only have a minute left on the test and still need to complete several questions, you should guess at random rather than leave them unanswered.
