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Re: General question about DS [#permalink]
06 Aug 2008, 06:26

brokerbevo may disagree with me, but I believe the actual solution to the problem can be different for each statement. The reason I believe this (not confirmed by GMAC as I've not really researched it all that much) is that a rule that they have to be the same must apply across all questions from simple to very complex. If you have a simple question like this (not that GMAT would have this one due to its simplicity):

Is X even?

1) x = 4 2) x + 1 = 6

Here, there are different values of x. Statement 1, x = 4 (obviously) and in Statement 2, x = 5. The point of DS questions is not to solve each equation or problem presented. The point of DS questions is to test our ability to recognize pertinent information when its presented. Do we know what information is necessary to solve a problem? If so, can you identify the necessary information as presented here? If so, have you been given enough pieces of the information to solve the problem?

It doesn't matter what the answer is. The answer to the problem could be "Yellow elephants with purple polka dots." But if one statement gave you enough information to be able to come up with that right answer, that statement is sufficient. The actual answers to the questions DO NOT MATTER. It only matters if you CAN answer it, not what the answer ACTUALLY is.

If the test authors can get you to take time to answer the question completely even after you know there is enough information to answer the question posed in the stem, then they've taken valuable seconds away from the 75 min alotted to take the test.

Hope I've helped make this disctinction clear.

durgesh - you found the thread where brokerbevo and I debated this very issue.

My take on it, and a I still stand behind it, is that if the statements contradict in the way brokerbevo says they cannot contradict, then the answer would be E.

Because if #1 is insufficient, and #2 is insufficient, and if together, you get different answers (i.e., the contradiction), that should be enough to answer the question because DS do not ask "Do the two statements below give the same answer?" DS asks "Do the statements below provide enough information to sufficiently answer the question posed by the stem?" Sometimes that question is "What is the value of x?" If you come up with 2 or more possible values for x in statement 1, and then 2 or more from statement 2, then if together you still come up with 2 or more possible answers, the answer will be E because the stem implies "What is the value of x?" means "Does the information presented below give you enough data to come up with one, and only one, value of x?"

Other times the stem calls for a yes/no answer. I used to make the mistake of when the answer was "No", like "Is x even?" and if x=5, then the answer would be "No, x is not even" - that would make me label that statement as insufficient. BUT IT'S NOT INSUFFICIENT. I was able to answer the question in the negative. Sufficiency is the ability to answer the question, not the ability to answer the question with "yes".

tarek99 wrote:

Guys, is it a fact that when we have option D as the answer in DS, then the answer from statement 1 and 2 must be the same or can they contradict?

_________________

------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Re: General question about DS [#permalink]
06 Aug 2008, 06:40

the doubt is specific to a situation when the option D is correct answer. I think if the statements contradict each other then we can not find the answer to the question... i'll take a very simple example..

what is x ?

1. x = 3 2. x = 4

both statements alone can answer the question "what is x" ..can we mark D.. no, becuase they contradict each other, we'll select E....

if i change the question to "Is x = 3 ?" then again statements are contradicting.... statement 1 : yes statement 2 : no

I've not seen such situation in OG or GMAT prep questions... so i guess its not possible on GMAT questions.

Re: General question about DS [#permalink]
06 Aug 2008, 06:54

How would the answer to your simple question be E? Statement #1 gives you enough information to answer the question "What is x?" The answer is "X is 3." And #2 gives you enough information to answer the question "What is x?" The answer is "X is 4". Here are the directions as written in the GMATPrep Software:

GMATPrep Software wrote:

What is measured? Data Sufficiency questions are designed to measure your ability to: - analyze a quantitative problem, - recognize which information is relevant, and - determine at what point there is sufficient information to solve the problem.

This says nothing about being able to solve the problem or equation presented.

GMATPrep Software DS Directions wrote:

Each Data Sufficiency problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. Using the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in July or the meaning of counterclockwise), you must decide whether the data given in the statements are sufficient for answering the question, then indicate one of the following answer choices: -Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked. -Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked. -BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient. -EACH statement ALONE is sufficient to answer the question asked. -Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

Looking at the language used in D, it makes me realize that you look at each statement ALONE. This means that it doesn't matter if #1 is x =3 and #2 is x = 4. Each one ALONE is sufficient to answer the question "What is the value of x?". If the directions did not include the word "ALONE" I think we could say that the answers cannot contradict each other, but since "ALONE", as used here, is the same as "INDEPENDENT" the relation of the two statements to each other does not matter with regard to an answer of D.

durgesh79 wrote:

the doubt is specific to a situation when the option D is correct answer. I think if the statements contradict each other then we can not find the answer to the question... i'll take a very simple example..

what is x ?

1. x = 3 2. x = 4

both statements alone can answer the question "what is x" ..can we mark D.. no, becuase they contradict each other, we'll select E....

if i change the question to "Is x = 3 ?" then again statements are contradicting.... statement 1 : yes statement 2 : no

I've not seen such situation in OG or GMAT prep questions... so i guess its not possible on GMAT questions.

_________________

------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Re: General question about DS [#permalink]
06 Aug 2008, 07:16

may be my example was too simple ... definetly it doesnt qualify to measure these 3 things - analyze a quantitative problem, - recognize which information is relevant, and - determine at what point there is sufficient information to solve the problem

all i can say is that i've not seen such contradictions on "good" DS questions and i hope i dont see it on the real GMAT....

Re: General question about DS [#permalink]
06 Aug 2008, 07:55

Yes, if I remember right, the distiction brokerbevo and I came to was that the answers CAN contradict each other, but GMAC CHOOSES not to put something on the exam in that does contradict. I was saying that from the structure of the test and the way the instructions are written, contradictory statements are POSSIBLE, but that doesn't mean GMAC allows it.

durgesh79 wrote:

may be my example was too simple ... definetly it doesnt qualify to measure these 3 things - analyze a quantitative problem, - recognize which information is relevant, and - determine at what point there is sufficient information to solve the problem

all i can say is that i've not seen such contradictions on "good" DS questions and i hope i dont see it on the real GMAT....

_________________

------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Re: General question about DS [#permalink]
06 Aug 2008, 09:18

Expert's post

If you see a question like:

What is x? 1) x^2 = 9 2) x^2 = 4

what could you possibly answer? Logically, C is good:

BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient.

because with both statements, no value of x can exist. But E seems good as well:

Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

because even with both statements, you can't find a value for x.

GMAC does not 'choose' to design DS statements to be logically consistent; it's a requirement. Otherwise questions can have two answers which are both logically correct, which can't happen on the GMAT. _________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: General question about DS [#permalink]
06 Aug 2008, 10:48

Quoting from Princeton Review "It is worth noting that we have never yet found a GMAT DS question where the correct answer was D and the two statements did not yield the same answer"

Logically I agree with jallenmorris. I guess its something that can happen but never does.

Re: General question about DS [#permalink]
08 Aug 2008, 05:41

IanStewart wrote:

GMAC does not 'choose' to design DS statements to be logically consistent; it's a requirement.

Can you show me in the instructions, or anything published officially by GMAC that DS are required to be consistent? The instructions I'm looking at state we are to consider each statement alone.

In your example below, I think the answer would be E. For statement #1, x = 3 or -3 so insufficient. In #2, x = 2 or -2, so insufficient. If you consider them together, then it doesn't help you figure out the value for x becuase the answer contradict each other, so the answer to the DS question should be E because together there is still not enough information to solve the question presented.

It seems that most people are forgetting the word "ALONE" in the instructions.

Step 1 - read the stem Step 2 - Read Statement #1 - determine if it provides enough information to answer the question stem. Step 3 - Forget all information presented in Statement #1 Step 4 - Read Statement #2 - determine if it provides enough information to answer the question stem. If #1 provided enough information to answer, for example What is the value of x? and if #1 make the value of x = 2, when considering Statement #2, we are not required to determine if Statement #2 makes the value of x = 2 simply because Statement #1's information made the value of x =2. Step 5 - If neither statement ALONE is sufficient to answer the question stem, then consider them together.

IanStewart wrote:

If you see a question like:

What is x? 1) x^2 = 9 2) x^2 = 4

what could you possibly answer? Logically, C is good:

BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient.

because with both statements, no value of x can exist. But E seems good as well:

Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

because even with both statements, you can't find a value for x.

GMAC does not 'choose' to design DS statements to be logically consistent; it's a requirement. Otherwise questions can have two answers which are both logically correct, which can't happen on the GMAT.

_________________

------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.