When you first learn GMAT Data Sufficiency, it seems fairly straightforward. Your task is to determine whether each statement gives you enough information to answer the question. So you look at the question, look at the statement, and think Yes, I can answer the question—sufficient or No, I can’t answer the question—insufficient.
As we get into it, though, we all realize that GMAT Data Sufficiency questions can be quite tricky. We find ourselves regularly looking at answer choices and thinking Oh, I didn’t see that way of doing it; how was I supposed to think of that? Fortunately, there are some concrete steps to improve your decisions on these tricky problems.
One of those steps is to realize that we have a language problem. When we say, “I can’t answer the question with this information,” we tend to process that as INSUFFICIENT, but that statement can actually mean two things. Sometimes it means “I can’t figure out an answer” and sometimes it means “I can’t answer it because there are multiple possible answers.” Those are very different!
In the first meaning, “I can’t figure out an answer,” it’s often a complex problem with multiple constraints. It might be one of those in which x has to be a multiple of one thing and have a certain remainder and meet some other requirement. You try out a couple numbers and nothing fits, so you say “I can’t figure out an answer,” but be careful! That does not all mean the statement is insufficient. You may not be able to figure out an answer, but somebody could!
The key thing is that insufficient means multiple possible answers. If the question is “What is x?” and the statement is “x = y + 2,” you might say, “I can’t figure out what x is,” but you’re really meaning that in the second way. There are multiple possible answers for x. It could be that x = 4 and y = 2 or x = 6 and y = 4 or so on and so on. That’s insufficient.
But back on the first meaning, when it’s just so complicated you can’t even come up with one, then you certainly haven’t found multiple answers! You’re actually closer to sufficient than you are to insufficient. All those constraints are making it hard for you to find a value that works, so it’s really unlikely that you could find two values that work, and you always need multiple answers to be insufficient.
What should you do then on GMAT Data Sufficiency? Drop the language of “I can’t figure it out.” Instead, focus on proving insufficient. If you find multiple possible answers, great, it’s proven. And if you can’t find multiple possible answers, whether you only find one possible answer or no possible answers at all, you guess sufficient. So, you end up with my favorite GMAT Data Sufficiency mantra: “Prove insufficient, guess sufficient.” 📝
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James Brock is a Manhattan Prep instructor based in Virginia Beach, VA. He holds a B.A. in mathematics and a Master of Divinity from Covenant Seminary. James has taught and tutored everything from calculus to chess, and his 780 GMAT score allows him to share his love of teaching and standardized tests with MPrep students. You can check out James’s upcoming GMAT courses here.