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# Must be True Approach

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Senior Manager
Joined: 27 Jul 2014
Posts: 272
Schools: ISB '15
GMAT 1: 660 Q49 V30
GPA: 3.76
Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 01:38
On average, plowed land erodes away at slightly more than 1 millimeter per year, while new soil builds up at about 0.2 millimeters per year. As a result, continually cultivated soil will become exhausted in the space of several hundred years, unless no-till agriculture is practiced. No-till agriculture is a method in which crop stubble remains in place and a special drill inserts the seeds into the soil. However, only about 16 percent of cultivated areas in the United States use this method.

Which of the following is best supported by the information above?

(A) Although the advance of farming technology has made no-till agriculture available to wealthy farmers, such methods are financially impractical for many American farmers.
(B) If the United States does not utilize means that replenish or reuse exhausted soil, it must eventually find other ways of getting agricultural products.
(C) Agricultural industries that do not require plowing - such as dairy or chicken farms - are not affected by topsoil erosion.
(D) If 5 out of 6 of all American farms were to practice no-till agriculture, the United States would produce enough agricultural products to meet domestic demand for several hundred years.
(E) Hydroponic farming (farming without soil) would solve the United States’ land erosion problem.

OA is B

I have doubt here

while going through concepts of must be true questions, its necessary that info in the correct answer needs to bevalidated by the info in the stimulus.
No new information outside the stimulus is correct

But here no where its present in Stimulus about the other ways getting products etc.

And this observation is not just for this particular question, i have seen this in a lot of questions i have gone through, that correct answer contains new information outside the stimulus.

Experts kindly let us know what is the correct approach to crack these must be true type questions

Kindly Suggest me some study material in order to get this approach correct
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Posts: 4488
Re: Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 10:40
kanigmat011 wrote:
On average, plowed land erodes away at slightly more than 1 millimeter per year, while new soil builds up at about 0.2 millimeters per year. As a result, continually cultivated soil will become exhausted in the space of several hundred years, unless no-till agriculture is practiced. No-till agriculture is a method in which crop stubble remains in place and a special drill inserts the seeds into the soil. However, only about 16 percent of cultivated areas in the United States use this method.

Which of the following is best supported by the information above?

(A) Although the advance of farming technology has made no-till agriculture available to wealthy farmers, such methods are financially impractical for many American farmers.
(B) If the United States does not utilize means that replenish or reuse exhausted soil, it must eventually find other ways of getting agricultural products.
(C) Agricultural industries that do not require plowing - such as dairy or chicken farms - are not affected by topsoil erosion.
(D) If 5 out of 6 of all American farms were to practice no-till agriculture, the United States would produce enough agricultural products to meet domestic demand for several hundred years.
(E) Hydroponic farming (farming without soil) would solve the United States’ land erosion problem.

OA is B

I have doubt here

while going through concepts of must be true questions, its necessary that info in the correct answer needs to be validated by the info in the stimulus.
No new information outside the stimulus is correct

But here no where its present in Stimulus about the other ways getting products etc.

And this observation is not just for this particular question, i have seen this in a lot of questions i have gone through, that correct answer contains new information outside the stimulus.

Experts kindly let us know what is the correct approach to crack these must be true type questions

Kindly Suggest me some study material in order to get this approach correct

Dear kanigmat011,
I'm happy to respond. First of all, when you post here or anywhere on GMAT Club, please cite the source. I looked this up: it's a Veritas question. Please never cite a question without its source. Also, as a general rule, it's considered bad form to post a question on GC that has already been posted. This particular question is discussed at length here:
plowed-land-erodes-away-at-slightly-more-than-1-millimeter-p-175237.html
You may find the answer to your question there.

Since you posted it here, in the Magoosh forum, I will respond. This is essentially a sound GMAT CR question---Veritas often writes good questions.

First I will say: there is a funny balance to appreciate about CR. On the one hand, you are perfectly correct: we are not expected, in any GMAT CR problem, to bring in outside knowledge about specific expertise in the issue discuss. Here, it would not be a good question if we had to have some kind of specialized knowledge in soil chemistry or some technical understanding of the dynamics of erosion to answer the question. That's clearly outside knowledge of a kind that is not necessary. BUT, in order to do well on GMAT CR, you have to have a very strong general sense of how the world works, of the ordinary push-and-pull of the everyday business world. Presumably, you are taking the GMAT because you want to earn an MBA and go into the business world. Think about all the facts that are part of everyday life for those people in the business world: that's what you need to know. How do you get that knowledge? Read the news. Read the Wall Street Journal and the New York Times. Read Bloomberg Businessweek and the Economist magazine. For more information, see the blog article:
https://magoosh.com/gmat/2014/gmat-crit ... knowledge/

Now in this question, I will simply point out that choices (A), (C), (D), and (E) are all unacceptable, so that narrows things quickly down to (B).

Here's the common-sense "outside knowledge" you need: the entire point of agriculture is that people grow food to eat. For tens of thousands of years, this has been the point of agriculture: the acquisition of food. That is a real-world fact that you need to know to understand GMAT CR.

Because of that, we can deduce that, right now, the USA practices a large amount of agriculture and gets a large amount of food from it: millions and millions of people are able to eat because of the agriculture practiced in America. The prompt talks about a problem that might drastically reduce the yield of American agriculture. Well, if these millions of people can no longer get there food from American agriculture, they will have to get their food from somewhere else.

Nothing in the question discusses the details of those "other ways of getting agricultural products," but these details are completely irrelevant. We don't need to have knowledge about that. It's much more basic.
Fact #1: the American people need food (should be obvious)
Fact #2: the American people current get food from agriculture (should be obvious)
Fact #3: soil erosion threatens American agriculture (presented in prompt argument)
Conclusion: If Americans can't get the food they need from their own agriculture, they will have to get it from somewhere else.
Once again, where or how the Americans would get the food at that point is irrelevant. That's outside. But the simple fact that the Americans would have to get the food they need from somewhere else is an inescapable conclusion.

Think about this in very practical terms. Suppose I tell you (a) tonight I am very hungry and intend to eat a big dinner, and I tell you (b) at the moment, I have no food in my apartment, then you can deduce that I definitely will not simply go home and eat dinner. I may go to a restaurant, or may go grocery shopping and bring food home, or etc. What I actually do is another issue, but the very simple issue is that you know, inescapably: if I don't have food at home, then I can't go straight home and eat dinner there. There is no outside knowledge needed to reach that simple conclusion.

This question is much the same, on the larger level. If Americans' current supply of food dwindles to nothing, they will need to get their food from someplace else. That simple observation is an inescapable conclusion. If we start asking about how American will get this other food, how they will purchase it or produce it, all that involves extra details, outside of the basic argument. The basic argument has the simple conclusion: they must get the food from somewhere else. That's a simple and logically self-contained conclusion.

If something in the answer choices causes you to ask additional questions that lead into outside knowledge, be careful: there's a big difference between whether outside knowledge is needed to evaluate the answer choice itself, vs. whether your own imagination drifts into places that require outside knowledge. Does this distinction make sense?

This question type, the "must be true," is sometimes called an inference or conclusion CR question. Here's a blog about them:
https://magoosh.com/gmat/2013/gmat-crit ... inference/

Does all this make sense?
Mike
_________________

Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Retired Moderator
Status: I Declare War!!!
Joined: 02 Apr 2014
Posts: 237
Location: United States
Concentration: Finance, Economics
GMAT Date: 03-18-2015
WE: Asset Management (Investment Banking)
Re: Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 11:57
Hi Mike!
Its more than crystal clear. I am not able to get fancy words in praise of that explanation of above questions.
I can understand that there is a time crunch with you, so if somehow you can come across where me or someone ask for an expert help, then please do explain those questions in a similar manner as you did just now.
I wish I know how to tag you... so that I could do in coming questions where your explanation needed.
Thanks
Celestial
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Posts: 4488
Re: Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 12:42
Celestial09 wrote:
Hi Mike!
Its more than crystal clear. I am not able to get fancy words in praise of that explanation of above questions.
I can understand that there is a time crunch with you, so if somehow you can come across where me or someone ask for an expert help, then please do explain those questions in a similar manner as you did just now.
I wish I know how to tag you... so that I could do in coming questions where your explanation needed.
Thanks
Celestial

Dear Celestial,
Thank you for your kind words! In general, I usually respond to most things in the Magoosh forum, so if you have a question, either post it as new thread in the Magoosh forum, or post a link here directing me to the thread in which a question appears.
Does this make sense?
Mike
_________________

Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Retired Moderator
Status: I Declare War!!!
Joined: 02 Apr 2014
Posts: 237
Location: United States
Concentration: Finance, Economics
GMAT Date: 03-18-2015
WE: Asset Management (Investment Banking)
Re: Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 12:49
Hi mikemcgarry !!!
Could you share the link where I can post question for you? As just magoosh link took me to its online course.
Or I should directly write your gmatclub username in my post, assuming it reaches you s a tag?
I am a proud magoosh user too!!
Regards
Celestial

mikemcgarry wrote:
Celestial09 wrote:
Hi Mike!
Its more than crystal clear. I am not able to get fancy words in praise of that explanation of above questions.
I can understand that there is a time crunch with you, so if somehow you can come across where me or someone ask for an expert help, then please do explain those questions in a similar manner as you did just now.
I wish I know how to tag you... so that I could do in coming questions where your explanation needed.
Thanks
Celestial

Dear Celestial,
Thank you for your kind words! In general, I usually respond to most things in the Magoosh forum, so if you have a question, either post it as new thread in the Magoosh forum, or post a link here directing me to the thread in which a question appears.
Does this make sense?
Mike
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Posts: 4488
Re: Must be True Approach  [#permalink]

### Show Tags

12 May 2015, 13:14
Celestial09 wrote:
Hi mikemcgarry !!!
Could you share the link where I can post question for you? As just magoosh link took me to its online course.
Or I should directly write your gmatclub username in my post, assuming it reaches you s a tag?
I am a proud magoosh user too!!
Regards
Celestial

Celestial:
My friend, let's distinguish three different things
1) The Magoosh website
2) The ad for Magoosh on GMAT Club
3) The Magoosh subforum on GMAT Club

I am suggesting that you post other questions as new threads in #3. This thread right now is in #3. If you go to the top of the page, you will see:
Attachment:

GMAT Club You are Here bar.JPG [ 18.59 KiB | Viewed 787 times ]

If you click on the word Magoosh in that bar, that will also lead you to #3.

If you write my name, or any user's name, that by itself is useless: writing a user's name doesn't give any notification to that user. BUT, if you use the "Mention this user" button to highlight a user's name when you are writing a post, then that user will be emailed a notification.

Does all this make sense?
Mike
_________________

Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Senior Manager
Joined: 27 Jul 2014
Posts: 272
Schools: ISB '15
GMAT 1: 660 Q49 V30
GPA: 3.76
Re: Must be True Approach  [#permalink]

### Show Tags

13 May 2015, 01:27
mikemcgarry wrote:
kanigmat011 wrote:
On average, plowed land erodes away at slightly more than 1 millimeter per year, while new soil builds up at about 0.2 millimeters per year. As a result, continually cultivated soil will become exhausted in the space of several hundred years, unless no-till agriculture is practiced. No-till agriculture is a method in which crop stubble remains in place and a special drill inserts the seeds into the soil. However, only about 16 percent of cultivated areas in the United States use this method.

Which of the following is best supported by the information above?

(A) Although the advance of farming technology has made no-till agriculture available to wealthy farmers, such methods are financially impractical for many American farmers.
(B) If the United States does not utilize means that replenish or reuse exhausted soil, it must eventually find other ways of getting agricultural products.
(C) Agricultural industries that do not require plowing - such as dairy or chicken farms - are not affected by topsoil erosion.
(D) If 5 out of 6 of all American farms were to practice no-till agriculture, the United States would produce enough agricultural products to meet domestic demand for several hundred years.
(E) Hydroponic farming (farming without soil) would solve the United States’ land erosion problem.

OA is B

I have doubt here

while going through concepts of must be true questions, its necessary that info in the correct answer needs to be validated by the info in the stimulus.
No new information outside the stimulus is correct

But here no where its present in Stimulus about the other ways getting products etc.

And this observation is not just for this particular question, i have seen this in a lot of questions i have gone through, that correct answer contains new information outside the stimulus.

Experts kindly let us know what is the correct approach to crack these must be true type questions

Kindly Suggest me some study material in order to get this approach correct

Dear kanigmat011,
I'm happy to respond. First of all, when you post here or anywhere on GMAT Club, please cite the source. I looked this up: it's a Veritas question. Please never cite a question without its source. Also, as a general rule, it's considered bad form to post a question on GC that has already been posted. This particular question is discussed at length here:
plowed-land-erodes-away-at-slightly-more-than-1-millimeter-p-175237.html
You may find the answer to your question there.

Since you posted it here, in the Magoosh forum, I will respond. This is essentially a sound GMAT CR question---Veritas often writes good questions.

First I will say: there is a funny balance to appreciate about CR. On the one hand, you are perfectly correct: we are not expected, in any GMAT CR problem, to bring in outside knowledge about specific expertise in the issue discuss. Here, it would not be a good question if we had to have some kind of specialized knowledge in soil chemistry or some technical understanding of the dynamics of erosion to answer the question. That's clearly outside knowledge of a kind that is not necessary. BUT, in order to do well on GMAT CR, you have to have a very strong general sense of how the world works, of the ordinary push-and-pull of the everyday business world. Presumably, you are taking the GMAT because you want to earn an MBA and go into the business world. Think about all the facts that are part of everyday life for those people in the business world: that's what you need to know. How do you get that knowledge? Read the news. Read the Wall Street Journal and the New York Times. Read Bloomberg Businessweek and the Economist magazine. For more information, see the blog article:
https://magoosh.com/gmat/2014/gmat-crit ... knowledge/

Now in this question, I will simply point out that choices (A), (C), (D), and (E) are all unacceptable, so that narrows things quickly down to (B).

Here's the common-sense "outside knowledge" you need: the entire point of agriculture is that people grow food to eat. For tens of thousands of years, this has been the point of agriculture: the acquisition of food. That is a real-world fact that you need to know to understand GMAT CR.

Because of that, we can deduce that, right now, the USA practices a large amount of agriculture and gets a large amount of food from it: millions and millions of people are able to eat because of the agriculture practiced in America. The prompt talks about a problem that might drastically reduce the yield of American agriculture. Well, if these millions of people can no longer get there food from American agriculture, they will have to get their food from somewhere else.

Nothing in the question discusses the details of those "other ways of getting agricultural products," but these details are completely irrelevant. We don't need to have knowledge about that. It's much more basic.
Fact #1: the American people need food (should be obvious)
Fact #2: the American people current get food from agriculture (should be obvious)
Fact #3: soil erosion threatens American agriculture (presented in prompt argument)
Conclusion: If Americans can't get the food they need from their own agriculture, they will have to get it from somewhere else.
Once again, where or how the Americans would get the food at that point is irrelevant. That's outside. But the simple fact that the Americans would have to get the food they need from somewhere else is an inescapable conclusion.

Think about this in very practical terms. Suppose I tell you (a) tonight I am very hungry and intend to eat a big dinner, and I tell you (b) at the moment, I have no food in my apartment, then you can deduce that I definitely will not simply go home and eat dinner. I may go to a restaurant, or may go grocery shopping and bring food home, or etc. What I actually do is another issue, but the very simple issue is that you know, inescapably: if I don't have food at home, then I can't go straight home and eat dinner there. There is no outside knowledge needed to reach that simple conclusion.

This question is much the same, on the larger level. If Americans' current supply of food dwindles to nothing, they will need to get their food from someplace else. That simple observation is an inescapable conclusion. If we start asking about how American will get this other food, how they will purchase it or produce it, all that involves extra details, outside of the basic argument. The basic argument has the simple conclusion: they must get the food from somewhere else. That's a simple and logically self-contained conclusion.

If something in the answer choices causes you to ask additional questions that lead into outside knowledge, be careful: there's a big difference between whether outside knowledge is needed to evaluate the answer choice itself, vs. whether your own imagination drifts into places that require outside knowledge. Does this distinction make sense?

This question type, the "must be true," is sometimes called an inference or conclusion CR question. Here's a blog about them:
https://magoosh.com/gmat/2013/gmat-crit ... inference/

Does all this make sense?
Mike

Thanks Mike for wonderful explanation.
Explanation really helped to understand the logic to be applied in these question.
Further I will keep in mind the guidelines for posting here
Re: Must be True Approach &nbs [#permalink] 13 May 2015, 01:27
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# Must be True Approach

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