* Quantitative Reasoning: Both tests assess mathematical skills. Topics like arithmetic, algebra, geometry, and data analysis are common to both. However, the specific questions, difficulty level, and emphasis on certain topics differ. The GRE often includes more advanced math concepts than the GMAT.
* Verbal Reasoning: Both tests include reading comprehension. However, the GRE includes two verbal sections: Reading Comprehension and Verbal Reasoning (which incorporates vocabulary in context and sentence equivalence questions). The GMAT's verbal section focuses on reading comprehension, critical reasoning, and sentence correction. While vocabulary is indirectly tested, the GMAT doesn't have explicit vocabulary questions like the GRE.
In short: There's a degree of overlap in the fundamental mathematical and reading comprehension skills tested, but the tests themselves are structured differently, with different question types and difficulty levels. You can't say a certain percentage of the syllabus is "the same." They assess similar skills but in distinct ways targeting different graduate programs.