Week 3 – Does Data Sufficiency make your head spin?

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As a contact-lens wearer, I occasionally have a rough morning when I put my contacts in the wrong eyes, mixing up left and right. This leads to an unpleasant few minutes where I can’t focus and my blurry vision starts to give me a headache. For me, the Data Sufficiency Questions on the Quantitative portion of the GMAT make me feel like I put my contacts in wrong. These questions are uncomfortable, annoying, and usually headache-inducing.

Not sure what a data sufficiency question is? Here’s an example:

If x is a positive integer, is x divided by 5 an odd integer?
1.)     x contains only odd factors
2.)     x is a multiple of 5

A)            Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B)            Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C)            BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D)            EACH statement ALONE is sufficient.
E)             Statement (1) and (2) TOGETHER are NOT sufficient to answer, and additional data is needed.

But, given that Data Sufficiency Questions will make up about 38-40% of the 37 Quantitative section questions, there’s no getting around these ones. From lots of practice and lots of missed questions, I’ve tried to learn from my mistakes:

Mistake #1: Reading the answer choices (A,B,C,D,E) – there’s not time! gmatblurry

Since all data sufficiency questions have the same answers, there’s no use reading them each time. I’m making sure that I know the answers and what they mean beforehand. Also, to avoid confusion and overwhelming myself with answers, I always start by setting myself up for process of elimination. For each D.S. question, I write 12TEN on my scratch pad. From there, I approach each statement and cross off answer possibilities as I go.

1 (Statement 1 only)
2 (Statement 2 only)
T (Together- both statements sufficient)
E (either statement alone sufficient
N (Neither)

You learn quickly that you can start crossing out answers as you evaluate statements. (For instance, if Statement 1 doesn’t work, you can cross off 1 & E).

Mistake #2: What is the question stem asking?

I always have to ask myself this it seems. Maybe with the time pressure, I feel like I need to go quickly onto the problem choices. There’s information in the stem that needs to be dealt with first though. Before you begin, ask if you’re looking for a Yes/No answer (i.e. is X=25) or a Value (what is x equal to?) This helps set the course so you know how far to solve. Which leads me to my next mistake:

Mistake #3: Don’t solve if you don’t need to!

My whole life I’ve been solving to the end of problems. I see an equal sign and a math equation and look for that one final number. In D.S. problems, many questions are just looking for the ability to answer. For instance, if a question asks “What is the value of x?”  and you have simplified an equation down to:  502x = 1975 – 2(20) , don’t waste time calculating for x. You know you can arrive at x, which is what the question is asking for. The correct answer would be how many statements you used to arrive at the final equation.

Mistake #4: Watch out for statements that give no new information.

Take this question for example:

Company X has a total of 400 employees. (addit’l information in question)…. What percentage of Company X employees received a raise?

1) 80 of Company X’s employees are managers.
2) 320 of Company X’s employees are not managers

Warning bells should be going off in your head right now. Even though the two statements are worded differently, they present the exact same information (giving numerical data on how many managers/non-managers are in the employee group). Don’t be fooled by the same statement simply re-packaged in a different format.

If all else fails with Data Sufficiency questions, and you’re simply stuck in a rut, take an educated guess. Hopefully though, by mastering some of your mistakes, you won’t have to resort to that. Good luck!