Hi buoyant,

Your "math" explanation is too complicated for the given scenario (even you're not sure what it means, which is problematic) and takes more time to use than other approaches. The Quant section of the GMAT is NOT a math test, it's a critical thinking test that uses math as the "gauge." You should remember that fact when approaching Quant questions; there's usually several approaches to answering the given question (the "math way" often takes the longest).

DS questions are often built around Number Properties (patterns behind the math and how numbers relate to one another). In Fact 1, since you know the definition of absolute value, your instinct should be to do the easiest thing that you can: say that a minus sign in front of an absolute value means the resulting value is either negative or 0. The left side of that equation creates either a 0 or positive result. Since the two terms are equal, the only possibility is 0.

Work to build up that skill (especially on DS questions) and you'd be amazed how your score can quickly improve and any pacing problem that you may have could disappear.

GMAT assassins aren't born, they're made,
Rich