Now, one of the ways to prove that you’re a candidate for the title of this post is if you’re saying to yourself right now “But I thought I wasn’t supposed to think about Statement 1 when I read Statement 2!!!”. While that’s true in a way – answer choices B and D require that statement 2 is sufficient ALONE, with no help from statement 1 – that’s part of that “not sufficient” knowledge of Data Sufficiency. Once you’ve established whether statement 2 is sufficient or insufficient alone, you also have a responsibility, on difficult questions, to consider whether it provides you with a clue as to something you may not have considered while looking at statement 1. If a statement says:
“x is an integer” – you’d better rethink whether you considered any nonintegers while looking at the other statement
“x is positive” – you’d better rethink whether you considered any negative numbers, or 0, while looking at the other statement
“Set J does not have a mode” – you’d better rethink whether you considered the terms in Set J could have repeated
And why doesn’t this violate the “consider each statement ALONE” logic? Because you’re not yet selecting an answer choice that uses them together – you’re just playing the game and thinking like the tentmaker. If you’re playing chess against a good player, and she attempts to move her bishop all the way across the board, lets her finger linger on it, and then suddenly retreats and moves her knight instead, you have to play the board as she played it – you play based on her bishop not having moved and her knight having moved. But you’d be a lousy player if you didn’t ask yourself “what was she trying to accomplish with her bishop” and “what did she see upon moving her bishop that scared her – where is she vulnerable”. That’s the same with Data Sufficiency – when statement 2 says “Set J doesn’t have a mode” you have to “play the board” based on statement 2 alone. But you’d be foolish not to consider whether statement 2 gives you any clues as to what you may need to think about with regard to statement 1.
The chess analogy works in large part because of that popular axiom “he’s playing chess while everyone else is playing checkers.” In order to score in the top 10% on the GMAT, you can’t simply be a checkers player…you have to be able to play some chess, a more strategic game. Checkers isn’t “wrong” – it’s just not sufficient. And on Data Sufficiency, the “checkers” strategies outlined above are correct – they’re just not complete and on difficult questions they’re not sufficient.
Think of it this way – in the above question, statement 2 was clearly not sufficient. Which means that the author of the question knowingly took options B and D off the table – no one should pick either choice. In doing so, the author took your quick-educated-guess odds from 1/5 to 1/3, giving you a substantial edge. How does he get his odds back? He makes the question hard – if one statement is easy, it means that the other probably requires some real thought. And that’s your chess-player’s clue – when a statement appears obvious, you should consider what it means for the question as a whole – how should that guide your analysis of the other statement.
Remember – to those who have done a few hundred Data Sufficiency problems and who are poised to score over 700, remembering “AD/BCE” or “1-2-T-E-N” isn’t hard. The concept of Data Sufficiency at the 75th-99th percentile level isn’t just about “can you cross-reference your analysis of the statements (i.e. 1 sufficient – 2 not sufficient – A!) with the answer choices to select the right level. It’s much more sophisticated – the Data Sufficiency setup lends itself to trap answers and to rewards for those who truly think critically. So play chess – don’t let yourself get overly confident with a basic understanding of Data Sufficiency. At least 10% of your competitors realize that that’s helpful, but it’s certainly not sufficient.
Brian Galvin is Director of Academic Programs at Veritas Prep, a GMAT prep and graduate school admissions consulting provider. Galvin writes a monthly column for Poets&Quants, offering typically contrarian advice for GMAT test takers.