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DS - Contradicting Statements

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DS - Contradicting Statements  [#permalink]

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New post 11 Apr 2019, 01:26
Hey guys!

I have question regarding an overall DS Strategy.

So I have read multiple timesaver know, that the two given statements in a DS question cannot contradict each other.

Let’s say a DS Question asks us whether x > 0?

If statement (1) establishes that this is allways true (Sufficient), Statement (2) cannot establish that this statement is allways wrong. So statement (2) could only also prove that the question is allways correct, or be insufficient.

Meaning a DS question like this would never exist:

Is x > 0 ?

(1) x+1 > 1
(2) x - 1 < -1

Because the two statements contradict each other.

My Question now is the following.

If I can somehow say a statement (1) is allways TRUE, isn’t one scenario for statement (2) in which the question is FALSE sufficient to prove that the solution is A?

The logic behind it being that statement (2) will not prove that the question is allways FALSE, as this would then contradict statement (1).

Because we have established that Statement (1) is correct (B, C and E are out) and that statement (2) alone cannot be sufficient without contradicting statement (1) (D is out as well) the answer has to be A.

This seems a little to good to be true as it would greatly reduce the workload for the statement (2) in many cases.

Am I missing something?
I hope I could express what I mean.
Should this topic already be discussed some place else, sorry for the repost and thank you for posting the Link to that post ;)

Thanks guys!

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Re: DS - Contradicting Statements  [#permalink]

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New post 11 Apr 2019, 07:05
1
Hi GMATDamon,

You actually bring up a really cool point, and I agree with what you are saying.

Take this example here: https://gmatclub.com/forum/is-x-y-1-x-y ... 35241.html

We are being asked "Is |x| = |y| ?"

Looking at statement (2), we can see that x = -y, and thus, using statement (2), we can say that YES |x| WILL ALWAYS EQUAL |y|, right?

Now looking at statement (1), which reads x - y = 6.

You may be tempted to say that whatever values you use for x and y, the answer will always be NO. However, since we are 100% certain that statement (2) is sufficient, there must be values of x and y such that statement (1) produces a NO answer and a YES answer.

(If you were wondering what those values are, when x = 3 and y = -3, we have answer of YES, and when x = 6 and y = 0, among others, we have an answer of NO.)

So, we can tell that statement (1) must be insufficient just by determining that there are values of x and y such the statement (1) produces a NO answer.

So although this method of solving a DS question works for only a small percentage of DS questions, it’s pretty cool to take the above approach, when applicable.
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DS - Contradicting Statements  [#permalink]

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New post Updated on: 11 Apr 2019, 13:41
1
Hi GmatDamon,

Welcome to gmatclub!

Is x > 0 ?
(1) x+1 > 1

x>0
Sufficient: YES, x>0. This is sufficient to answer the question

AD

(2) x - 1 < -1
x<0
Sufficient: NO, x is NOT >0. This is sufficient to answer the question

D

However, you will not see such a question on gmat as statements (1) and (2) contradict to each other. Read here:

https://gmatclub.com/forum/data-suffici ... 30500.html
http://www.gmathacks.com/data-sufficien ... other.html
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Originally posted by Akela on 11 Apr 2019, 08:27.
Last edited by Akela on 11 Apr 2019, 13:41, edited 1 time in total.
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Re: DS - Contradicting Statements  [#permalink]

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New post 11 Apr 2019, 09:17
GmatDamon wrote:
Hey guys!

Am I missing something?
I hope I could express what I mean.
Should this topic already be discussed some place else, sorry for the repost and thank you for posting the Link to that post ;)

Thanks guys!

Posted from my mobile device

This question is already discussed in one of my posts. So, click here.
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Re: DS - Contradicting Statements  [#permalink]

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New post 11 Apr 2019, 09:44
GmatDamon wrote:
Hey guys!

I have question regarding an overall DS Strategy.

So I have read multiple timesaver know, that the two given statements in a DS question cannot contradict each other.

Let’s say a DS Question asks us whether x > 0?

If statement (1) establishes that this is allways true (Sufficient), Statement (2) cannot establish that this statement is allways wrong. So statement (2) could only also prove that the question is allways correct, or be insufficient.

Meaning a DS question like this would never exist:

Is x > 0 ?

(1) x+1 > 1
(2) x - 1 < -1

Because the two statements contradict each other.

My Question now is the following.

If I can somehow say a statement (1) is allways TRUE, isn’t one scenario for statement (2) in which the question is FALSE sufficient to prove that the solution is A?

The logic behind it being that statement (2) will not prove that the question is allways FALSE, as this would then contradict statement (1).

Because we have established that Statement (1) is correct (B, C and E are out) and that statement (2) alone cannot be sufficient without contradicting statement (1) (D is out as well) the answer has to be A.

This seems a little to good to be true as it would greatly reduce the workload for the statement (2) in many cases.

Am I missing something?
I hope I could express what I mean.
Should this topic already be discussed some place else, sorry for the repost and thank you for posting the Link to that post ;)

Thanks guys!

Posted from my mobile device


Can you share an official question, which you have come across and then relate your point to that question?
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Re: DS - Contradicting Statements   [#permalink] 11 Apr 2019, 09:44
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