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A Modest Proposal for GMAT Data Sufficiency Strategy

Shake things up to dominate GMAT DSI want you to forget everything you know about GMAT data sufficiency.

Okay, well, maybe not everything. But let me flip things on their head for a second. This may just be the fresh look you need to dominate GMAT data sufficiency once and for all.

I was working with a student last week who was struggling to evaluate Statement #2 in isolation (If you don’t know what I’m talking about, review our Data Sufficiency – Part 1 lesson for the step-by-step methodology you should use when attacking GMAT DS questions). It can be tough to “forget” what you learned in Statement #1, let’s be honest. And then my student said something astute: It’s almost like the GMAT test makers deliberately build on Statement 1 with what they put in Statement 2, he said.

So I gave him this advice: Why not start by evaluating Statement #2 first?

The more I’ve been thinking about it, the more this strategy makes sense to me.

Consider this simplistic but illustrative example:

What is x?

(1) x² = 25
(2) x > 0

Evaluating Statement #1 in isolation quickly reveals that it’s not sufficient to answer the question. As a quadratic equation, it yields two possible values for x (+5 and -5), not just one, so we can’t definitively answer the question.

But look what happens when you then try to evaluate Statement #2 in isolation. You’re biased! You’ve already determined that x is either +5 or -5, so look at what Statement #2 tells you! It helps you to choose between them, right? Clearly x = +5 so Statement #2 is sufficient to answer the question! ….

… Well, not exactly. In fact, not at all. Statement #2 is only sufficient when you’ve factored in what you first saw in Statement #1. By itself, Statement #2 is not sufficient. If x > 0, then there are an infinite number of possible values of x that would satisfy that inequality. But it can be hard to remember that when your brain is still influenced by what it saw in Statement #1.

So why not just start with Statement #2? Think about how much more obvious it would have been that simply knowing x>0 is not enough to answer the question if you hadn’t seen Statement #1 yet! At the end of the day, there’s really no benefit to evaluating Statement #1 first. All that’s important is that you evaluate each statement in isolation before considering them together, since much of the time you never will have to get that far anyway (i.e. the correct answer will be A, B, or D).

So here’s my modest proposal: If you’re having trouble evaluating Statement #2 in isolation without taking Statement #1 into account…switch things up and start with Statement #2.

Now you might be thinking to yourself, how is that any different? Won’t I then have the same problem when I proceed to evaluate Statement #1 after already having seen what’s in Statement #2?

I don’t believe so and here’s why. First of all, I think my student may have a good point. I’ve looked at thousands of GMAT data sufficiency questions over the years, and whether it’s deliberate or not on the part of the GMAC, Statement #2 does often seem to “build on” what’s in Statement #1 — especially when the correct answer ends up being C. More than that, however, our brains are wired to think linearly (or vertically in this case). It’s perfectly natural for us to proceed smoothly from Statement #1 to Statement #2. We’ve been starting with #1 on tests our entire lives, after all! But starting with #2? Blasphemy! That just makes no sense! Which is exactly why you should do it. Your brain is much less likely to naturally assume that Statement #1 follows logically from Statement #2 than the other way around. The correct answer may in fact end up being C, but you’ll have to arrive at that conclusion the right way — having evaluated each statement in isolation first — rather than accidentally assuming the two statements work together just because you couldn’t quite get your mind to separate the two.

At the end of the day, you should be evaluating each statement independently before considering them together. So why not start with Statement #2? There’s nothing that says you can’t, and doing so may just prevent you from making careless mental errors and thus get more right answers on GMAT data sufficiency questions, thereby boosting your entire score. Go on, give it a try! What do you have to lose?

Like what you just read? Disagree? Think I’m crazy? Leave your questions and comments below!