Brian Galvin is the Director of Academic Programs at Veritas Prep, where he oversees all of the company's GMAT prep courses.
Conventional business wisdom suggests that "there is no such thing as a free lunch," and "if it seems too good to be true, it probably is." When we make decisions, we should always be on the lookout for "What's the catch?" as the world is full of ploys to entice us with offers that look great on the surface, but contain underlying (and maybe even underhanded) catches that swing the favor away from us.
The authors of the GMAT -- in part because of their desire to ensure that top MBA students are those who are leery of these too-good-to-be-true offers and can navigate them successfully -- use these ploys themselves to lure you in to bad answer choices the same way that others may try to lure you in to bad investments or commitments. The key, then, on the GMAT as in life, is to ask yourself, "What's the catch?"
Commonly, "the catch" rears its ugly head on Data Sufficiency questions, in which you're asked by the GMAT to determine when you have enough information ("When is the information sufficient?") to make a definitive decision in answer to the question. In these questions, the writers of the exam can provide you with what seems to be sufficient information to make your decision, but do so by "hiding" the catch, or the types of information for which the answer would be different.
Consider the question:
Is x <0?
(1) |x| = -x
(2) x^2 > 0
The first statement seems to suggest that x has to be negative, as it notes that the absolute value of the variable is the same as multiplying that variable by -1. If x were positive, its absolute value would be positive, but by multiplying it by -1 you'd end up with a negative, so the statement wouldn't hold. For any negative number, taking its absolute value is the same as multiplying it by -1, so the statement does hold. However, one number fits neither category (negative or positive), and must be considered on its own. "Absolute value" simply means "distance from zero," so the absolute value of 0 is 0; there is no distance between the value 0 and 0. Similarly, multiplying 0 by anything, including -1, leaves us with 0, so statement one holds for all negative numbers, but also for 0, and statement one is not sufficient.
To finish the question, the second statement is true for all numbers except 0 (0 squared is still 0), so it on its own is not sufficient. Taking both statements together, however, we find that the first statement allows for numbers that are either less than or equal to zero, and the second statement eliminates 0, so the correct answer is C, as with both statements together we can determine that x must be less than 0.
More importantly to your study is the takeaway: in this question, 0 was "the catch." If you didn't consider it, you would likely have answered "A" incorrectly, assuming that x had to be negative. The authors of the GMAT know that, when you're thinking quickly, it's easier to overlook numbers such as 0 -- or non-integers, or other values that don't fall within your typical day-to-day thought process -- and they will often use these numbers to create a trap. On the GMAT, as in life, remember to try to spot the catch before you make any final decisions, and you'll have a higher degree of success by being wary of statements (or offers) that seem too good to be true.
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