DS Understanding - 1) and 2) must agree with each other. - The Beat The GMAT Forum

DS Understanding - 1) and 2) must agree with each other.

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uwhusky: Legendary Member; Posts: 1172; Joined: Wed Apr 28, 2010 6:20 pmFollowed by: 4 members; Thanked: 74 times

by uwhusky » Thu Aug 12, 2010 10:45 am

I have been running into few issues with this, and I want to make sure I have the right information in regards to DS questions on the actual GMAT.

If a solution can be found with 1), does 2) at minimum require to work with the same solution?

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Source: Beat The GMAT — Data Sufficiency | Thu Aug 12, 2010 10:45 am

Brian@VeritasPrep: GMAT Instructor; Posts: 1031; Joined: Thu Jul 03, 2008 1:23 pmFollowed by: 255 members; Location: Malibu, CA; Thanked: 716 times; GMAT Score:750

by Brian@VeritasPrep » Thu Aug 12, 2010 11:39 am

Hey uwhusky,

Yes - and this concept can be quite useful for you on the GMAT, so I'm glad you brought it up.

Statements 1 and 2 MUST BE consistent with each other.

Think about it - one of the more popular answer choices for a lot of these questions is C, both statements together are sufficient. If it weren't possible to get the same answer using both statements together, the GMAT has lost a plausible answer choice...it just can't afford to do that.

So if Statement 1 is sufficient to give you an answer, statement 2 must allow for that same answer to be true.

Let's try a quick example to see how it can be useful:

What is the value of x?

1) x^2 = 81

2) -x > 7

Say you looked at statement 1 and thought that it meant "x = 9". Statement 2 tells you that x < -7, which means that it cannot be 9. This discrepancy means that you have to go back and reconsider the statements - you did something wrong, because they have to be consistent.

Looking back, you may notice that x^2 = 81 means that x could be 9 or -9. Using statement 2, you'd find that x must be -9, and C is the correct answer (which it could not have logically been if the statements were allowed to be inconsistent).

Simply put, if statements 1 and 2 seem to contradict, go back and check your work because that means you did something wrong.

Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep

Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.

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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members; Thanked: 32 times

by Gurpinder » Thu Aug 12, 2010 12:57 pm

hmmm....this always popped in my head when i did those questions.

and now thanks to u 2, it is confirmed.

"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Thu Aug 12, 2010 1:09 pm

Great points from Brian above. I'd just add that you will sometimes see *unofficial* questions posted in forums which come from dubious sources and which do not obey this principle - that is, you will see some questions posted here where the statements are *not* consistent. If you notice that, you can be certain you're looking at a question from a question designer who doesn't understand the GMAT, so you can safely skip such questions and move on to more relevant material.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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uwhusky: Legendary Member; Posts: 1172; Joined: Wed Apr 28, 2010 6:20 pmFollowed by: 4 members; Thanked: 74 times

by uwhusky » Thu Aug 12, 2010 3:08 pm

Ian Stewart wrote:Great points from Brian above. I'd just add that you will sometimes see *unofficial* questions posted in forums which come from dubious sources and which do not obey this principle - that is, you will see some questions posted here where the statements are *not* consistent. If you notice that, you can be certain you're looking at a question from a question designer who doesn't understand the GMAT, so you can safely skip such questions and move on to more relevant material.

Thank you for confirming the "exact" thought I have in my mind!

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