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Intern  Joined: 17 Oct 2019
Posts: 1
GMATPrep - Data Sufficiency Problems  [#permalink]

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Does anyone have a strong structure for how to approach DS problems? In terms of minimum data to solve the problem, and not wasting the time to try and solve it with I and then II and then combined? I'm afraid of wasting time getting actual answers to DS problems, not simply answering the 'sufficiency' question.

Two Three examples:

First Example:
Is sqrt((x-3)2 ) = 3-x?
Given:

x≠3

-x|x| > 0

What is the smartest way to approach the problem? After getting it wrong on a practice test, I can see why the answer is what it is; but not how to come to that conclusion in a time-efficient manner.

Second Example:
In the x-y plane, does y=3x+2 contain (r,s)?
Given:

(3r+2-s)(4r+9-s)=0(4r-6-s)(3r+2-s)=0

Here, I'm at a bit of a loss - is the right approach to plug it into I, and recognize either 3r+2-s could be 0, or 4r+9-s could be? And a similar conclusion for II, but 4r+9-s and 4r-6+s cannot both be zero for a given (r,s)? Basically, do I have to accept this one is going to take longer than the target time?
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GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: GMATPrep - Data Sufficiency Problems  [#permalink]

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Hi ChinusGomes,

Data Sufficiency is a question type that is unique to the GMAT - and many Test Takers find DS to be challenging at some point - so you're not alone. Thankfully, DS is predictable and you can train to take advantage of how those questions are written. That having been said, just like any other GMAT question, you will have to put in some effort (and do a certain amount of work on your pad) to make sure that you prove what the correct answer is.

DS questions are interesting because they're built to 'test' you on a variety of skills (far more than just your 'math' skills), including organization, accuracy, attention-to-detail, thoroughness and the ability to prove that your answer is correct. DS questions also have no 'safety net' - meaning that if you make a little mistake, then you will convince yourself that one of the wrong answers is correct. Thankfully, the 'math' behind most DS questions isn't that complicated, but you have to be thorough with your work and take advantage of any 'shortcuts' that are built into the prompt for you to find.

Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying and your goals:

Studies:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?

Goals:
4) What is your overall goal score?
5) When are you planning to take the GMAT?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?

GMAT assassins aren't born, they're made,
Rich
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Re: GMATPrep - Data Sufficiency Problems  [#permalink]

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Bunuel
I think , this one is not the perfect place/forum to ask this question. Better if this link is shifted to perfect forum.
Thanks__
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“The heights by great men reached and kept were not attained in sudden flight but, they while their companions slept, they were toiling upwards in the night.”

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Joined: 04 Dec 2015
Posts: 851
GMAT 1: 790 Q51 V49 GRE 1: Q170 V170 Re: GMATPrep - Data Sufficiency Problems  [#permalink]

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ChinusGomes wrote:
Does anyone have a strong structure for how to approach DS problems? In terms of minimum data to solve the problem, and not wasting the time to try and solve it with I and then II and then combined? I'm afraid of wasting time getting actual answers to DS problems, not simply answering the 'sufficiency' question.

Two Three examples:

First Example:
Is sqrt((x-3)2 ) = 3-x?
Given:

x≠3

-x|x| > 0

What is the smartest way to approach the problem? After getting it wrong on a practice test, I can see why the answer is what it is; but not how to come to that conclusion in a time-efficient manner.

Second Example:
In the x-y plane, does y=3x+2 contain (r,s)?
Given:

(3r+2-s)(4r+9-s)=0(4r-6-s)(3r+2-s)=0

Here, I'm at a bit of a loss - is the right approach to plug it into I, and recognize either 3r+2-s could be 0, or 4r+9-s could be? And a similar conclusion for II, but 4r+9-s and 4r-6+s cannot both be zero for a given (r,s)? Basically, do I have to accept this one is going to take longer than the target time?

A more detailed overview is also at the beginning of each of the MPrep Quant Strategy Guides.

I'll give a very quick outline here, and run through your second problem:

1. Understand the question. This might mean simplifying the math, translating the question into plain English, etc.

In the x-y plane, does y=3x+2 contain (r,s)?

You can tell that a line contains a point, if you can plug the coordinates of the point into the equation of the line, and get a correct result. So, what this is really asking is the following:

Does s = 3r + 2?

Also, note that this is a yes/no question. To answer it, you don't need to know the exact values of s and r. You only need to know whether s = 3r + 2 or not.

2. Pick a statement and understand it.

Statement 1: (3r+2-s)(4r+9-s)=0

This looks like a product of two expressions. I know that if the product of two expressions equals 0, then one or both of those expressions has to equal 0. So, what this is really telling me, is:

Either 3r + 2 - s = 0, OR 4r + 9 - s = 0, or both.

Simplify the math a bit:

Either s = 3r + 2, or s = 4r + 9.

3. Figure out whether that statement gives you enough info to answer the question. Eliminate wrong answers.

One possibility is that s = 3r + 2; in that case, the answer to the question would be 'yes'. But, there's another possibility, that s = 4r + 9. In that case, I don't know whether or not s = 3r + 2, so I couldn't answer the question. Since I'm not sure that I can answer the question, it's insufficient. So, I eliminate A and D (because 1 is insufficient.)

4. Repeat with the other statement:

(4r-6-s)(3r+2-s)=0

Either s = 4r + 6, or s = 3r + 2

But, I don't know which. So, insufficient as well. Eliminate B.

5. If necessary, put the two statements together.

I now know two things. First, I know that s equals either 3r + 2, or 4r + 9. Second, I know that s equals either 3r + 2, or 4r + 6.

The only possibility that matches both of these is that s equals 3r + 2. If s didn't equal 3r + 2, then it would have to equal 4r + 9 (to make the first statement true), but it would also have to equal 4r + 6 (to make the second statement true.) Since those can't both be true, that's impossible. So, the only possibility, given that both statements have to be true at the same time, is that s = 3r + 2. Since you know that, you know the answer to the question is 'yes', so the statements together are sufficient and the answer is C.
_________________ Chelsey Cooley | Manhattan Prep | Seattle and Online

My latest GMAT blog posts | Suggestions for blog articles are always welcome! Re: GMATPrep - Data Sufficiency Problems   [#permalink] 07 Nov 2019, 12:33
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