16 Feb 2017

GMAT Basics: Data Sufficiency Part II

Data Sufficiency Value vs Yes/No Questions

For my last article I introduced DS (Data Sufficiency) questions and discussed the topic in general. I’m going to do a series of articles on DS delving into it’s intricacies. For this article we’re going to talk about the two basic flavors of DS questions.

Before we move on I just want to remind all y’all (yes, I’m from Texas) that DS questions are really asking you what combination of statements give you sufficient information to answer the question. The question you read is the condition that must be checked, it isn’t the real question. Basic DS questions are annoying enough as regular “value” questions that ask “how much,” or “what is the value.” The other basic type of DS questions are “Yes/No” quesitons. These questions ask whether something is or is not true, not what is the value. The funny thing about Y/N questions is whether it’s true or not doesn’t matter, only that you can give a definitive answer.

Let me give you a couple examples and show how question wording changes the approach and the outcome.

First, a simple “value” DS question.

If x is an integer, what is the value of x?

1) x² < 4

2) x > 0

Here your job is to figure out what combination of statements given allows you to find a value for x. If you look at statement 1 you know that x can be +1, -1, or 0. So not enough info to answer the question. If you look at statement 2 you know x can be all positive integers. Again, not sufficient. But together, statement 1 and 2 combined, you know that x has to be +1. So the answer is C, 1 & 2 together. Remember, all you need to know is that you can give a definitive answer, you don’t actually need to know what is the value of x.

And now for almost the same question but in “Y/N” style.

If x is an integer, is x < -2?

1) x² < 4

2) x > 0

For this one the question asks you if x is less than -2. The real question is what combination of statements allows you to say “yes” only or “no” only. Statement 1 is sufficient. x can be +1, -1, or 0, all instances that are greater than -2, which means the answer is always “no.” Statement 2 is sufficient. x is never less than -2, which means the answer is always “no.” In this case, the correct answer choice is D.

You can see that the questions can seem very similar but have different approaches and different answers. Until you get used to these mechanics, these questions may feel alien for a while. My suggestion, as always, is to prep well and prep hard. Having a good coach can be beneficial and I’m always here to help. If you have any questions contact me at [email protected].