What is Quantitative Comparison on the GRE? How do I approach it?

Quantitative Comparison (QC) gives you two quantities, Quantity A and Quantity B, and asks which is greater (or if the relationship can't be determined). Your four answer choices are always the same: A is greater, B is greater, they're equal, or it can't be determined. The key approach is to simplify both sides, test different values when variables are involved, and recognize when the answer depends on the values chosen.