Identical Data Sufficiency Statements
September 15, 2008The GMAT rewards mental flexibility, and nowhere on the test is that more true than Data Sufficiency. Whether you're looking at the question itself or one of the two statements, it's always worthwhile to simplify.
This is especially important because DS questions will occasionally give you the same piece of information in two different ways. Just because two choices look different doesn't mean they are different.
This example is fairly simple, but it illustrates the point:
What is the value of a?(1) a - b = 6
(2) b = a - 6
When you simplify the second statement, you discover it is identical to "a - b = 6."
Which DS Choices?
When this happens, the only possible correct answers are (D) and (E). If one statement is sufficient on its own, the other statement must be sufficient on its own. (After all, they're the same!) In that case, the correct choice is (D).
If one statement is insufficent on its own, the other must be as well. Since you don't gain any advantage by putting them together, they remain insufficient even when combined, so the answer is (E).
In the example above, the correct choice is (E).
How Often Does This Occur?
Most of the time, there's no structural trickery of this sort in DS questions. But it's always a possibility, especially on multi-variable algebra problems like the example given above. The odds are low that you'll see more than one situation like this out of the 13 DS questions on your exam.
That one time, though, be ready to eliminate the first three choices. Expect--at least occasionally--to see a DS question in which both statements say the same thing.
Jeff Sackmann is a GMAT tutor based in New York City. He has created many resources for GMAT preparation, including the popular GMAT Math Bible and GMAT Verbal Bible, as well as 1,800 practice GMAT math questions.
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