Here is a data sufficiency question. It is a question on slopes of lines and tests basic concepts about lines in geometry and coordinate geometry.QuestionAre lines p (with slope m) and q (with slope n) perpendicular to each other?1. m + 2 = n2. m + n = 0Correct Answer: Choice C. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER … [Read more...] about GMAT DS : Geometry, Coordinate Geometry