The GMAT has 3 sections: Analytical Writing, Quantitative, and Verbal.
Quantitative
Knowledge of the following:
 Arithmetic: Properties of integers, fractions, decimals, ratios and proportions, percents, and powers and roots of numbers
 Basic algebra: Simplifying and manipulating algebraic equations, solving linear equations, solving quadratic equations, manipulating expressions with exponents and inequalities, absolute value, and functions
 Basic geometry: Lines, convex polygons, triangles, quadrilaterals, circles, rectangular solids, cylinders, and coordinate geometry
 Word problems: Rates, work, mixtures, interest (simple and compound), profit, and sets (overlapping groups)
 Statistics: Probability, sets, counting methods (combinations and permutations), mean, median, mode, range, and standard deviation
 Ability to apply knowledge of the above.
 Ability to differentiate between information that is relevant to solving a problem and information that is irrelevant.
GMAT Quantitative questions come in two forms: Problem Solving and Data Sufficiency...

Problem Solving questions require you to solve for an answer to a question and then select that answer from amongst five answer choices. Click here to see a sample Problem Solving question.

Data Sufficiency questions require you to determine whether information given in the two statements accompanying a problem provide enough information to find an answer to the question asked. Click here to see a sample Data Sufficiency question.
Verbal
Verbal reasoning tests your reading and language skills, as well as your ability to do the following:
 Comprehend written material
 Understand logical relationships between points in a passage
 Identify and use correct grammatical expression as it relates to the following:
 Proper use of modifiers
 Pronoun agreement and clarity
 Parallel construction of lists and comparisons
 Verb tense and agreement
 Correct usage of idiom
GMAT Verbal questions come in three forms: Sentence Correction, Critical Reasoning, and Reading Comprehension.

Sentence Correction questions require you to determine which of five answer choices provide the clearest, most concise and grammatically correct version of a portion underlined in a sentence. Click here to see a sample Sentence Correction question.

Critical Reasoning questions require you to assess information given in a passage and determine the correct answer from five choices to a question using logical reasoning. Click here to see a sample Critical Reasoning question.

Reading Comprehension questions require you to read and understand the information given in a passage and use that information to determine which of five choices is the correct answer to each question about that passage. Click here to see a sample Reading Comprehension passage and question.
Because the GMAT is at base a reasoning test, both sections also assess the following skills:
 Time management
 Analytical and Critical Thinking
 Logical Reasoning
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