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Data Sufficiency Strategy

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Data Sufficiency Strategy

by ynatchev » Wed Feb 27, 2013 11:43 pm
Hello all,

I just read this article posted by Brent about a strategy to the Data sufficiency questions. https://www.beatthegmat.com/mba/2013/02/ ... ment-28429

Please can you tell me if I'm getting his argument right. We only need to determine if the statments are suffiecient to answer the question, not if the answer to the question is Correct or NO. Is that correct?

Thanks in advance and also special thanks to Brent for his article.
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by Brent@GMATPrepNow » Thu Feb 28, 2013 7:57 am
All we need to concern ourselves is whether or not each statement is sufficient to answer the target question.

Do we care if the answer to the target question is YES, NO, 8, pi, or sqrt(7)?
No, we don't.
All that matters is whether or not there's one unique answer to the target question.

I hope that helps.

If anyone is interested, our entire Data Sufficiency module (consisting of 16 videos and over 1 hour of instruction) is free for everyone: https://www.gmatprepnow.com/module/gmat-data-sufficiency

Cheers,
Brent
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by David@VeritasPrep » Thu Feb 28, 2013 11:33 am
Ynatchev - You seem to be discovering one of those truths about data sufficiency - "sometimes you do not have to do the math!" But you must be careful with this knowledge as it very often gets people into trouble.

Please read this article about when to do the math on data sufficiency and when you can answer without doing the math. https://www.beatthegmat.com/mba/2012/12/ ... ufficiency

This may help you:

Think of yes or no questions not as "sufficient" or "not sufficient" but as "consistent" or "not consistent."

This means that so long as the various possibilities allowed by a particular statement are consistent that statement is sufficient. So if you find that x could equal -10, 0, or 14 and if the question asked is x > 20? This would be consistent as each value gives you a "NO, not greater than 20?"

For specific number questions, of course "sufficient" means "specific" as in just one value. This is usually easier for students to naturally comprehend. It is the Yes/ no questions that cause more trouble!
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by ynatchev » Fri Mar 01, 2013 12:24 am
Thank you guys for the clarification :)

Brent please let me know if i understood you right. For example if we have a problem that asks "Is x>10"
1)x=6
2)x=12
In this case 1) is sufficient right? because it answers the target question is x>10 (although the answer is No its not greater than 10)
For 2) the same it is SUFFICIENT (and it is greater than 10)

So the final answer would be in a Data sufficiency question that D) both statements alone are sufficient

Please correct me if I'm wrong


David thank you for your reply. What I meant is that of course some problems require you to do the math to find out if it is sufficient or not, but you do the math to the point when it gives you an idea that you can actually answer the target question, in order to see if it is sufficient or not.

My question here was, as I wrote to Brent, even though the answer to is x>10 and in statement 1 it says x=6, which obviously is less than 10. So the answer to the question "Is x>10" is NO x is not greater than 10 in the first Statement. But is is sufficient SURE . So my orginal question was if Statement 1 does not satisfy the target question because its less than 10, it is still sufficient right?

Again please correct me if I understood you both wrong. And thanks again for the useful tips :)
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by David@VeritasPrep » Fri Mar 01, 2013 4:31 am
On data sufficiency "no" is just as good as "yes."

I see what you mean by "satisfy the question" by that you mean obtain an answer of "yes". In your example, statement 2 gives you a "yes" so it satisfies because x > 10.

But on the GMAT you are not trying to prove the statement true you are just trying to obtain a consistent answer. So your statement 1) is also sufficient because x is never > 10 so we have a consistent answer.

The statement that would not be sufficient is statement 3) 7<x<15 in this case you would get a "no" because values 8 and 9 and even 10 are not > 10. And you would get a "yes" as values 11, 12, 13, etc. are greater than 10. So a "no" and a "yes" is not sufficient.

One more thing. I would not use the phrase "satisfies the target question" because the question is not something that you seek to satisfy. You just want an answer and that is it. You do not care if x > 10 or not. This is one of the more common misconceptions about data sufficiency.
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by ynatchev » Fri Mar 01, 2013 5:13 am
I'm glad you understood what I meant David and thank you for your answer :) Ok now I can be calm that even though I get an answer of NO it is still sufficient to answer the question (if it is consistent)

David thanks for the example too, I get it. When we can't say for sure if x<10 or x>10 (from your example of 7<x<15) then it is not sufficient cause we have values that are under and above 10.

Thanks again guys your awesome :)

So in conclusion in Data Sufficiency section what we are trying to tell is if it is sufficient or not? (not if it answers the question with Yes or NO)
On the other hand in Problem solving (we need an Yes only :))
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by David@VeritasPrep » Fri Mar 01, 2013 7:11 am
Here are some more thoughts for you on data sufficiency.

This is on divising a strategy for not making silly errors:
https://www.beatthegmat.com/mba/2012/10/ ... -handrails

This is on the fact that the two statements must allow some common value:
https://www.beatthegmat.com/mba/2012/01/ ... ufficiency


Good luck! Remember Data Sufficiency is fun. Perhaps the most enjoyable of all the GMAT question types. It is infinitely varied and never boring!
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