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DS - First Timer

This topic has 2 expert replies and 1 member reply
Valerieangelkos Newbie | Next Rank: 10 Posts
Joined
08 Apr 2013
Posted:
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DS - First Timer

Post Wed May 15, 2013 5:04 pm
Hi,
I have a question regarding DS questions.
If the choice, either (1) or (2), gives an answer to a specific question, being YES or NO, should I choose it because it gives a specific answer, or because the answer it gives is YES?

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Top Reply
Post Fri May 17, 2013 8:38 am
A definitive YES or a definitive NO answer would each be sufficient. Only an answer of MAYBE (or "sometimes yes, sometimes no") would be insufficient.

However, "definitive NO is sufficient" is not a rule that the GMAT tests regularly. For most YES/NO questions, a statement that gives sufficient information will give a "yes" answer to the question.

Out of the DS problems in OG13 and the Quant Supplement 2nd Ed, only 1 that I can find has statements that give a definitive "no" answer:

Quote:
DS #136 OG13
If @ represents one of the operations +, -, and x , is k @ (L + m) = (k @ L) + (k @ m) for all numbers k, L , and m ?

(1) k @ 1 is not equal to 1 @ k for some numbers k.

(2) @ represents subtraction.
(The actual problem used a circle, not an @ symbol, but I don't know how to recreate that here!)

We can rephrase the question as "does the operation @ represent multiplication?" as multiplication is the only operation for which k @ (L + m) = (k @ L) + (k @ m)

(1) k @ 1 is not equal to 1 @ k for some numbers k.

If these two are not equal, then @ must NOT represent multiplication, because k*1 = 1*k. Therefore, the answer to the question "is @ multiplication?" is "no, definitely not." Sufficient.

(2) @ represents subtraction.

Again, the answer to the question "is @ multiplication?" is "no, definitely not." Sufficient.

The answer is D.

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fcabanski Master | Next Rank: 500 Posts
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Post Fri May 17, 2013 8:13 am
The statement is sufficient if it answers the question. If the question is a yes/no question, and the statement lets you know the answer is no, then the statement is sufficient.

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Post Fri May 17, 2013 8:38 am
A definitive YES or a definitive NO answer would each be sufficient. Only an answer of MAYBE (or "sometimes yes, sometimes no") would be insufficient.

However, "definitive NO is sufficient" is not a rule that the GMAT tests regularly. For most YES/NO questions, a statement that gives sufficient information will give a "yes" answer to the question.

Out of the DS problems in OG13 and the Quant Supplement 2nd Ed, only 1 that I can find has statements that give a definitive "no" answer:

Quote:
DS #136 OG13
If @ represents one of the operations +, -, and x , is k @ (L + m) = (k @ L) + (k @ m) for all numbers k, L , and m ?

(1) k @ 1 is not equal to 1 @ k for some numbers k.

(2) @ represents subtraction.
(The actual problem used a circle, not an @ symbol, but I don't know how to recreate that here!)

We can rephrase the question as "does the operation @ represent multiplication?" as multiplication is the only operation for which k @ (L + m) = (k @ L) + (k @ m)

(1) k @ 1 is not equal to 1 @ k for some numbers k.

If these two are not equal, then @ must NOT represent multiplication, because k*1 = 1*k. Therefore, the answer to the question "is @ multiplication?" is "no, definitely not." Sufficient.

(2) @ represents subtraction.

Again, the answer to the question "is @ multiplication?" is "no, definitely not." Sufficient.

The answer is D.

_________________


Ceilidh Erickson
Manhattan Prep GMAT & GRE instructor
EdM in Mind, Brain, and Education
Harvard Graduate School of Education


Manhattan Prep instructors all have 99th+ percentile scores and expert teaching experience.
Sign up for a FREE TRIAL, and learn why we have the highest ratings in the GMAT industry!

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