When you take your GMAT test it will be 'computer adaptive'. This means that the testing software adapts to your performance as you progress through the exam. It is essential for you to understand how computer adaptive testing works and learn test taking strategies to tackle the test in order for you to achieve a high score.
Does my score start at 0?
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. If you answer the question correctly you will be given a more difficult question which is worth more points; but answer it incorrectly and the next question you are given will be easier and worth fewer points, which will have a negative impact on your score.
Can I go back and check my answers?
Because each right or wrong answer you give directly affects the next question the test shows you, the CAT does not allow you to go back to questions you've already answered and double-check your work. The CAT will only show you one question at a time and does not allow you to see the next question until you've answered the current one. So, double-check your answer choice before moving on. Once you've noted and confirmed your answer, that's it.
That being said, if you cannot answer a question, you should definitely guess. Guess intelligently and strategically—i.e., eliminate any answer choices that you know to be wrong and then guess from those remaining. Remember, you will be penalised for every question that you do not answer. If you only have a minute or two left, and several questions remaining, you should guess at random rather than leave them unanswered.