Data Sufficiency

Ian (Number Theory guy, I saw it in your small bio... very impressive, congrats!) and all others:

I guess I needed the "Bertrand´s Postulate" to answer another BTG post here a couple of minutes ago (related to the link below)...could you go there and see if you are able to justify the same thing without using high-tech machinery? Thanks!

Link: https://www.beatthegmat.com/my-wrong-ones-t68806.html

Thanks to Ian and fabio.
I rest my case, since my evidence ( flowchart) has been discounted for justifiable reasons.

(P.s: @ testluv if the flowchart were true, then my case was that you will not encounter contradiction in the C answer domain, and as far as your example goes there is no possible contradiction in there anyways).

Hi magnus,

yes, there was indeed a possibility of contradiction in the example I provided. If you take the view that contradiction is possible, then in my example x can be both positive and negative at the same time, and you would have to choose E. My further point was that because the statements can't contradict E is not correct. Finally, because the GMAT must be consistent, this must mean that we must always assume away any possibly contradictory information between the two statements regardless of whether we are in A, B, C, D or E domain, and regardless of the flowchart depicted in the OG book (and regardless of the fact that we woudn't even be considering the statements in conjunction in A, B or D domains).

Anyways, I am very happy that you have resolved your issue.

Allow me to sum up by saying we can always make two (and only two) assumptions in GMAT DS questions:

(1): the statements always provide true information
(2): the statements can never provide necessarily contradictory information.

magnus opus wrote:Thanks to Ian and fabio.
I rest my case, since my evidence ( flowchart) has been discounted for justifiable reasons.

Uau, I am happy to "hear" that, magnus. I am sure it would be a pleasure to help you prepare for your GMAT quant exam personally (presencial classes, I mean), but I guess you do not live in Sao Paulo, Brazil, right?!

Let´s do the following: please register in my e-course (link below) and I will have the pleasure to put at your disposal my first two e-classes for free, ok?! I really believe that you will like it a lot and, if so, it would be great for me to have someone like you recommending my prep!!

Thank you for your good-will and your "out-of-the-box mental flexibility" to consider (Ian´s and) mine´s positions as "justifiable"!

Regards,
Fabio.

As far as Data Sufficiency problems are concerned, I guess there still leaves a small (nice) detail to be "brought to light"... doing that, I guess all our readers (and I guess we have a record here, don´t we?) will have the full DS survival package...

The detail is the following:

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No (correctly created) Data Sufficient problem may be solved before the statements are presented,
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I mean: it is impossible to find a UNIQUE solution before using the statements.

This is NOT stupid, by the way, because THE important consequence of this fact is the following:

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therefore if a statement does not add info to the question stem, it is certainly insufficient to answer the question asked!
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Example 01:

If.... , is ....... ?

(1) One week has seven days

We are sure sttm (1) is not enough to answer the question asked, because it does not add new info to the question stem, and we know (by above) that the question stem itself is not enough to answer the question presented inside itself!



Example 02:

If x is odd, is ...... ?

(1) x is an integer

We are sure sttm (1) is not enough to answer the question asked, because from the fact that is known that x is odd, then it is known that x is an integer, so that again sttm (1) does not add new info to the question stem.


Well, that´s it. I hope you all like it.

Regards,
Fabio.

Testluv wrote:Hi magnus,

yes, there was indeed a possibility of contradiction in the example I provided. If you take the view that contradiction is possible, then in my example x can be both positive and negative at the same time, and you would have to choose E. My further point was that because the statements can't contradict E is not correct. Finally, because the GMAT must be consistent, this must mean that we must always assume away any possibly contradictory information between the two statements regardless of whether we are in A, B, C, D or E domain, and regardless of the flowchart depicted in the OG book (and regardless of the fact that we woudn't even be considering the statements in conjunction in A, B or D domains).

Anyways, I am very happy that you have resolved your issue.

Allow me to sum up by saying we can always make two (and only two) assumptions in GMAT DS questions:

(1): the statements always provide true information
(2): the statements can never provide necessarily contradictory information.

no, there is more to it, i have my gmat really soon, so dont have time, but once its i promise to come back to this post and point out why..

fskilnik wrote:As far as Data Sufficiency problems are concerned, I guess there still leaves a small (nice) detail to be "brought to light"... doing that, I guess all our readers (and I guess we have a record here, don´t we?) will have the full DS survival package...

The detail is the following:

----------------------------------------------------------------------
No (correctly created) Data Sufficient problem may be solved before the statements are presented,
-----------------------------------------------------------------------

I mean: it is impossible to find a UNIQUE solution before using the statements.

This is NOT stupid, by the way, because THE important consequence of this fact is the following:

---------------------------------------------------------------------
therefore if a statement does not add info to the question stem, it is certainly insufficient to answer the question asked!
---------------------------------------------------------------------

great point, fskilnik.

If we're creating a DS "survivalist package" then let me quickly thrown in another tip.

If a statement provides you with useless information, then it is obviously insufficient, and also the answer cannot be C.

For example:

If x is even, is y odd?

(1) x is an integer.

Now, clearly (1) is insufficient on at least two counts. First, we should notice right away that the question is about the status of y, and (1) provides no information about y. However, (1) is completely useless because it is not giving us any information that we didn't already know from the question stem. Since evenness/oddness is only a property of integers, then of course x is an integer.

When we combine useless information with insufficient information, clearly we still have insufficiency. So whatever (2) might have said, the answer cannot be C.

magnus: best of luck on your GMAT!