The GMAT exam is divided into 4 sections,
GMAT Test Section||
# of Questions||
Analysis of Argument|
(Argument is from list of essays available on the GMAT website)
Integrated Reasoning (IR)||
Two-Two Part Analysis
The total exam duration is roughly around 3 hr 30 min. You get two optional 8 min breaks after the Integrated Reasoning and Quant Section.
The marks of the Analytical Writing section are reported between 1-6. You can easily score >5, if you argument is properly structured. Refer to chinese burned gmat essay guide.
The IR section is score from 1-8.
The Quant & Verbal section are both scored from 1-51. The combined Quant & verbal score is used to calculate your score out of 800.
All the questions are important. You have to answer all the questions. GMAT places a very heavy penalty for not completing the exam. Since, the exam is adaptive so the initial questions on the section have higher weightage( but the exact algorithm of the exam is not known). GMAT itself mentions that the algorithm is self correcting hence by the end of the exam it will try to judge your level and give questions accordingly.
Further Read about What are the key skills and books to be used for GMAT preparation?
At the end of the GMAT exam, GMAT now allows you to view your unofficial score before you decide to submit or cancel your score. See the official announcement