Data Sufficiency: More About The Qs Than As
Upon first glance, the trickiest thing about Data Sufficiency questions is their answer choices – unlike most multiple choice math questions you’ve seen, these don’t contain “possible answers to the question” as answer choices, but rather “descriptions of whether or not you have enough information.” It’s a unique style of question and one that takes some time to get used to. So when you see:
- Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked;
- Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked;
- Both statements (1) and (2) TOGETHER are sufficient to answer the question asked; but NEITHER statement ALONE is sufficient.
- EACH statement ALONE is sufficient to answer the question asked;
- Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
It’s certainly understandable that you’re grasping for ways to make that process easier. Whether it’s “AD/BCE” (a helpful process-of-elimination chart that breaks apart the families of answer choices along “Statement 1 is sufficient / Statement 1 is not sufficient”) or “1-2-TEN” (1 sufficient; 2 sufficient; together sufficient; either sufficient; neither sufficient), most students feel substantially more confident when they’ve finally memorized and internalized the answer choices and have a process to work through.
But remember the key word in Data Sufficiency – Sufficiency. Understanding the answer choices is necessary, but it’s not at all sufficient to help you ace the quant section. And the glaring mistake that many test takers make is thinking that once they’ve mastered the answer choices they’re good to go on Data Sufficiency.
In actuality, that’s not true at all – knowing the answer choices is the price of admission to these questions, not a sign of mastery. Data Sufficiency questions are not merely a unique way to ask a math question – they’re a logic puzzle unto themselves. And your key to success largely includes this: get to a point where you can forget about the answer choices and focus on the most underrated portion of the problem: the question stem itself.
The Question Stem
The GMAT loves misdirection – like a magician can force your attention away from his sleight of hand, the GMAT can very deftly attract your attention away from a key portion of the question. And one of the author’s favorite tricks is to embed a crucial but “innocent-looking” piece of information in the question stem, knowing that your AD/BCE – 1-2-TEN thought process places you in a hurry to get to the statements and the answer choices. So while your attention is pointed downhill, the test can quickly slip past an important fact in the question stem. Consider the example:
If xy ≠ 0, what is the value of x?
- yx2 + 4xy + 4y = 0
- y = 6
If you race to attack the quadratic in statement 1, you may miss a very important part of the question – that line that xy ≠ 0 means that neither x nor y can be 0. And that means that as you attack statement 1, the factored-out equation y(x + 2)(x + 2) = 0 does not have a solution for y – since y isn’t 0, you can divide both sides by y and recognize that (x + 2)(x + 2) = 0, so x must be -2. But if you didn’t see that little question stem caveat, you could easily have thought that you needed statement 2, selecting C instead of the correct A.
More importantly, take the lesson from this that it’s crucial for you to unpack all of the information provided in the question stem. The question stem often hides crucial nuggets of information like:
- xy < 0 > exactly one of x and y is negative
- A merchant is selling hats > “hats” cannot be negative or nonintegers, so you’re dealing with a nonnegative whole number
- The area of square ABCD is 16 > you know that the sides are 4, the diagonal is 4√2, the perimeter is 16, all angles are 90 degrees…
Question stems often include much more information than meets the eye – that portion above the statements isn’t just the question, it can also be chock full of information that makes the problem interesting. So be certain to mine that question stem for details.
Questions > Answers
More largely, keep in mind that understanding Data Sufficiency answer choices is only the first step – a critical step, of course, but a fundamental one – toward mastering Data Sufficiency. It may well take practice, but don’t pat yourself on the back simply for memorizing the answer choices. AD/BCE and 1-2-TEN are helpful tools, but they’re not quite the strategic weapons that many consider them to be. Your goal should be to use those tools to make the answer choices a nonfactor as you take the test, so that you can turn your attention back from the bottom of the screen to the top – the less you have to think about the answer choices, the more you can focus on the elements of Data Sufficiency problems that really make these problems difficult, and the most-often overlooked element is the question stem itself. Difficult Data Sufficiency questions are far more often “won” in the question stem than in the answer choices.
Brian Galvin is Director of Academic Programs at Veritas Prep, a GMAT prep and graduate school admissions consulting provider. This is his second column for Poets&Quants.com. His contrarian views appear monthly.