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# Exposure to certain chemicals commonly used in elementary schools as

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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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26 Oct 2018, 04:04
This 'NOT' in option C is confusing me.

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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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29 Nov 2018, 06:48
1
GMATNinja wrote:
The author concludes that one of two things has happened over the past ten years: either 1) Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or 2) they are more sensitive to the chemicals than schoolchildren were ten years ago. How does the author arrive at this conclusion?

• We are given that exposure to cleaners and pesticides commonly used in schools can cause allergic reactions in some children.
• Over the past ten years, the proportion of schoolchildren sent to school nurses for allergic reactions to THOSE chemicals has increased significantly.

The author states two possible explanations for this increase, but are those the only options? The author's explanation will only hold up if one of the following is assumed:

Quote:
(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

A change to the number of nurses doesn't impact the number of students sent to see the nurses, so (A) can be eliminated.

Quote:
(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

We are not concerned with allergies to other substances. Regardless of whether children allergic to the chemicals are more likely to have allergies to other substances, we still need to explain why more students are now sent to the nurses because of reactions to THOSE chemicals. The two theories in the conclusion are only meant to explain the increase in the number of schoolchildren sent to the nurses because of THOSE chemicals, so choice (B) is irrelevant.

Quote:
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

According to the argument, the increase in the proportion of schoolchildren sent to the elementary school nurses is due to either greater exposure to the chemicals or a greater sensitivity to the chemicals. But what if children who have allergic reactions to the chemicals are more likely to be sent to a school nurse now than they were ten years ago? Maybe the amount and severity of the allergic reactions was the same ten years ago but students were simply less likely to be sent to the nurse back then. Maybe ten years ago the teachers simply let the suffering students remain in class with watery eyes and running noses (for example).

That could explain the increase in the proportion of schoolchildren sent to the elementary school nurses, even if students' exposure and sensitivity to the chemicals has not changed. In order for the argument to hold, the author must assume that children who have allergic reactions to the chemicals are NOT more likely to be sent to a school nurse now than they were ten years ago. Choice (C) looks good.

Quote:
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

Perhaps the cleaners ARE commonly used in houses and apartments, but we don't care about WHERE the students were exposed to the chemicals. If exposure has increased, whether at school or at home, then the author's argument would be valid. The author does not say that exposure has increased AT THE SCHOOLS, so choice (D) can be eliminated.

Quote:
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

We are trying to explain an increase in the PROPORTION of students sent to the nurses, not an increase in the TOTAL NUMBER of students sent to the nurses. Thus, an increase in the number of students or the proportion of the population attending elementary schools does not matter. We need to explain the increase in the PROPORTION sent to the nurses for those allergic reactions. Choice (E) is not a required assumption and can be eliminated.

Choice (C) is the best answer.

However, I didn't understand E.
Can you expand a bit more on PROPORTION VS TOTAL?
I think TOTAL has an effect on PROPORTION.
Can you explain with a little example(mathematically or in any way) where I'm wrong?
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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06 Dec 2018, 21:04
Akshit03 wrote:
GMATNinja wrote:
The author concludes that one of two things has happened over the past ten years: either 1) Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or 2) they are more sensitive to the chemicals than schoolchildren were ten years ago. How does the author arrive at this conclusion?

• We are given that exposure to cleaners and pesticides commonly used in schools can cause allergic reactions in some children.
• Over the past ten years, the proportion of schoolchildren sent to school nurses for allergic reactions to THOSE chemicals has increased significantly.

The author states two possible explanations for this increase, but are those the only options? The author's explanation will only hold up if one of the following is assumed:

Quote:
(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

A change to the number of nurses doesn't impact the number of students sent to see the nurses, so (A) can be eliminated.

Quote:
(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

We are not concerned with allergies to other substances. Regardless of whether children allergic to the chemicals are more likely to have allergies to other substances, we still need to explain why more students are now sent to the nurses because of reactions to THOSE chemicals. The two theories in the conclusion are only meant to explain the increase in the number of schoolchildren sent to the nurses because of THOSE chemicals, so choice (B) is irrelevant.

Quote:
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

According to the argument, the increase in the proportion of schoolchildren sent to the elementary school nurses is due to either greater exposure to the chemicals or a greater sensitivity to the chemicals. But what if children who have allergic reactions to the chemicals are more likely to be sent to a school nurse now than they were ten years ago? Maybe the amount and severity of the allergic reactions was the same ten years ago but students were simply less likely to be sent to the nurse back then. Maybe ten years ago the teachers simply let the suffering students remain in class with watery eyes and running noses (for example).

That could explain the increase in the proportion of schoolchildren sent to the elementary school nurses, even if students' exposure and sensitivity to the chemicals has not changed. In order for the argument to hold, the author must assume that children who have allergic reactions to the chemicals are NOT more likely to be sent to a school nurse now than they were ten years ago. Choice (C) looks good.

Quote:
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

Perhaps the cleaners ARE commonly used in houses and apartments, but we don't care about WHERE the students were exposed to the chemicals. If exposure has increased, whether at school or at home, then the author's argument would be valid. The author does not say that exposure has increased AT THE SCHOOLS, so choice (D) can be eliminated.

Quote:
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

We are trying to explain an increase in the PROPORTION of students sent to the nurses, not an increase in the TOTAL NUMBER of students sent to the nurses. Thus, an increase in the number of students or the proportion of the population attending elementary schools does not matter. We need to explain the increase in the PROPORTION sent to the nurses for those allergic reactions. Choice (E) is not a required assumption and can be eliminated.

Choice (C) is the best answer.

However, I didn't understand E.
Can you expand a bit more on PROPORTION VS TOTAL?
I think TOTAL has an effect on PROPORTION.
Can you explain with a little example(mathematically or in any way) where I'm wrong?

Always remember: what are we being asked, and what information is relevant to answering that question? On CR, we could clarify math until a great proportion of cows come home, and still be no closer to picking the right answer choice.

But to avoid any confusion, let's clarify some math! Or at least some terminology.

Generally speaking, "proportion" is a portion, or percentage, of the total. It's typically expressed as a percentage or fraction.

Let's say that I have 10 tomatoes in my garden. I'm asked, "Charles! Did your daughter eat a greater proportion of the tomatoes than you did today?" I look back at our tomato diary, which shows:

• I ate 1 tomato, which is 10% of the tomatoes (1/10).
• My daughter ate 5 tomatoes, which is 50% of the tomatoes (5/10). She loves those things even more than I do. (And for a 20-pound beast, she sure can eat.)

But holy nightshade! I miscounted, and it turns out that my garden actually had 20 tomatoes before we started eating.

• This means that I actually ate 5% of the tomatoes (1/20).
• And my daughter actually ate 25% of the tomatoes (5/20).
• Nobody ate any more tomatoes. But since the total number of tomatoes changed, our measurement of the proportion of tomatoes eaten changed as well.

So yes, the absolute number of tomatoes affects the number used to describe the proportion of tomatoes eaten.

But did this help me answer the question? Nope.

I was basically asked, "Who ate a bigger share of however many tomatoes you had?"

And changing the total number of tomatoes will never change the answer: "My daughter ate a bigger proportion of tomatoes. And I'm terrible at counting things in my garden."

Now let's look at choice (E):

Quote:
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

This choice basically compares a % measured ten years ago to a % measured today.

The actual numbers are never mentioned. If 5% of Renston's population attended elementary school ten years ago, and 5% of Renston's population attends elementary school today, then any of the following could be true:

• 5 out of 100 people in Renston attended elementary school ten years ago.
• 270 out of 5,400 people in Renston attended elementary school ten years ago.
• 20 out of 400 people in Renston attended elementary school today.
• 250 out of 5,000 people in Renston attended elementary school today.

The assumption presented by (E) doesn't tell us anything about the total number of students in either time period. The total numbers could have grown or shrunk to literally any size with zero impact on what (E) is stating.

More importantly, the type of proportion that (E) describes is totally irrelevant to the argument we're analyzing.

The author is trying to explain the proportion of elementary school students sent to nurses for treatment of allergic reactions:

• This proportion is a % of elementary school students.
• In a fraction, it would be expressed as [# of elementary students sent to the nurse for treatment of specific allergic reactions] / [total # of elementary students].

Choice (E) describes the proportion of elementary students in Renston:

• This proportion is a % of people in Renston.
• In a fraction, it would be expressed as [total # of elementary students] / [total number of people in Renston].

I hope this clarifies what I meant when explaining why (E) is not a required assumption! I didn't mean to say that totals have no place in measuring proportion. But in the case of this question, knowing the totals never matters, and in the case of choice (E), the proportions and totals being discussed are simply irrelevant to the author's argument.
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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23 Apr 2019, 07:21
I'm glad that i chose the right answer (c) but i really struggled a lot and it took me a lot of time.

I noticed that i struggle with negative modifiers with degrees such as "not more likely". When i really thought about this phrase it just means it is NEUTRAL. So when I substituted "not more likely" with the idea of it being just neutral. I understood it more.

As a non native english speaker, i struggle with tricky negative words like the one above.

Does anyone have tips with tricky words like this?

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Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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Updated on: 23 Dec 2019, 16:00
3
Sooner or later, I am hoping someone will discover these back-page responses I am giving to the Question of the Day series. My take:

Key points: The question asks about an assumption that must be made to qualify the argument, so we need to read between the lines. The argument itself has to do with schoolchildren and chemicals, so that relationship will need to be addressed in the correct answer.

Breakdown: As is often the case in these CR questions, the first line of the passage sets the stage with background information; the next line delivers more information that seems to be building toward something; the final line delivers the essential information, here the argument on which the question is based. The second line should not be glossed over: a higher proportion of children, compared to ten years ago, is receiving treatment from nurses for allergic reactions to the chemicals from sentence one. What could explain this trend?

Answers: I like to highlight weak points in the responses to mimic the way I process them as I read.

(A) The number of school nurses... has not decreased

Analysis: The schoolchildren are left out entirely from consideration, and the focus is shifted to the nursing staff instead. Is it necessary to assume that the number of nurses has not decreased in order for this higher proportion of chemical-allergic children to become qualified? Of course not. It could be the case that there really are more children who are developing allergies to the chemicals, regardless of what may be going on with the nurses. This is a classic GMAT™ sleight of hand. Red light.

(B) no more likely than other children...

Analysis: Why do we need to compare schoolchildren and the types of allergies they have to explain why more children have been visiting the nurses for a specific allergic reaction? The thought had not even crossed my mind until now. As soon as I reached "other substances," I knew this response had completely gone off the rails. Red light.

(C) Children are not sent to the nurses now any more than they used to be for allergic reactions to "the chemical"

Analysis: The "not" gives reason for pause. To join the question and the response, we need to understand that the assumption is that children with an allergic reaction to these specific chemicals are sent to see the nurses with about the same frequency that they used to be sent. If that were NOT true--i.e. that the children were being sent more frequently for some other reason, such as that identification of symptoms had gotten better in the past decade, or any of a number of reasons--then no assumption would need to be made. We would have the facts or evidence we needed instead. This is an answer that checks the necessary boxes: there are more schoolchildren visiting the nurses compared to ten years ago, but we have to assume that the information in the response is accurate for it to be so. Green light.

(D) The chemicals are not commonly used

Analysis: Who cares how often the chemicals are used, particularly in houses and apartment buildings--non-school locations? I will be honest in saying that as soon as I had decided on (C), I quickly skimmed this choice and (E) and confirmed (C). Why must we assume that the chemicals in question are applied less commonly in locations other than the school for the argument to work? This is a clear distraction, nothing more. Red light.

(E) Children do not make up a larger proportion of Renston's population

Analysis: Whether children do or do not make up a larger proportion of the general population, it is not necessarily the case that more of them, a greater proportion, would experience allergic reactions to "the chemicals" used in the schools. You should know from the Quant sections that proportions without context are meaningless. We could use numbers to disprove such an assumption, as in the following exercise:

Allergic Schoolchildren (10 years ago)
2/10 (100 total children in Renston, pop. 10,000)

Allergic Schoolchildren (present)
3/10 (100 total children in Renston, pop. 9,000)

Okay, so the target group represents a higher proportion of Renston's decreasing population. So what? Why would their numbers have to have increased relative to the population of the entire town in order for the argument to hold its weight? We could just as easily have held the population steady at 10,000, which would show that whether or not the children make up a larger proportion of the total population of Renston, the fact of the matter is that a larger proportion of them is now visiting school nurses due to allergic reactions to certain chemicals. Thus, choice (E) has no bearing on the question, but it is trickier to navigate than some of the other choices. Yellow light.

Guessing: Choices (A), (B), and (D) all represent easy targets or red light answers. The first option, (A), leaves out the target group, the schoolchildren, and offers up information on nurses instead; meanwhile, (B) and (D) both go left of center without ever getting off the ground, providing information that is not related to the argument--other substances, other locations. (C) discusses the target group and offers a reasonable explanation as to why a greater proportion of schoolchildren would be visiting the nurses. Choice (E), although attractive at first glance, could go either way with actual numbers standing in to create proportions. At least the answer choices should be whittled down to (C) or (E), and with that kind of 50/50 on your plate, always look to disprove any part of one response or the other, rather than choose what feels better or resembles the wording of the paragraph more.

Happy studies.

- Andrew

Originally posted by MentorTutoring on 08 Jul 2019, 17:38.
Last edited by MentorTutoring on 23 Dec 2019, 16:00, edited 1 time in total.
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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18 Nov 2019, 06:54
GMATNinja wrote:
The author concludes that one of two things has happened over the past ten years: either 1) Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or 2) they are more sensitive to the chemicals than schoolchildren were ten years ago. How does the author arrive at this conclusion?

• We are given that exposure to cleaners and pesticides commonly used in schools can cause allergic reactions in some children.
• Over the past ten years, the proportion of schoolchildren sent to school nurses for allergic reactions to THOSE chemicals has increased significantly.

The author states two possible explanations for this increase, but are those the only options? The author's explanation will only hold up if one of the following is assumed:

Quote:
(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

A change to the number of nurses doesn't impact the number of students sent to see the nurses, so (A) can be eliminated.

Quote:
(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

We are not concerned with allergies to other substances. Regardless of whether children allergic to the chemicals are more likely to have allergies to other substances, we still need to explain why more students are now sent to the nurses because of reactions to THOSE chemicals. The two theories in the conclusion are only meant to explain the increase in the number of schoolchildren sent to the nurses because of THOSE chemicals, so choice (B) is irrelevant.

Quote:
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

According to the argument, the increase in the proportion of schoolchildren sent to the elementary school nurses is due to either greater exposure to the chemicals or a greater sensitivity to the chemicals. But what if children who have allergic reactions to the chemicals are more likely to be sent to a school nurse now than they were ten years ago? Maybe the amount and severity of the allergic reactions was the same ten years ago but students were simply less likely to be sent to the nurse back then. Maybe ten years ago the teachers simply let the suffering students remain in class with watery eyes and running noses (for example).

That could explain the increase in the proportion of schoolchildren sent to the elementary school nurses, even if students' exposure and sensitivity to the chemicals has not changed. In order for the argument to hold, the author must assume that children who have allergic reactions to the chemicals are NOT more likely to be sent to a school nurse now than they were ten years ago. Choice (C) looks good.

Quote:
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

Perhaps the cleaners ARE commonly used in houses and apartments, but we don't care about WHERE the students were exposed to the chemicals. If exposure has increased, whether at school or at home, then the author's argument would be valid. The author does not say that exposure has increased AT THE SCHOOLS, so choice (D) can be eliminated.

Quote:
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

We are trying to explain an increase in the PROPORTION of students sent to the nurses, not an increase in the TOTAL NUMBER of students sent to the nurses. Thus, an increase in the number of students or the proportion of the population attending elementary schools does not matter. We need to explain the increase in the PROPORTION sent to the nurses for those allergic reactions. Choice (E) is not a required assumption and can be eliminated.

Choice (C) is the best answer.

But in A, the number of nurses matters? Because if the nurses number decrease, the proportion will be increase though after total number of students will not increase. So,shouldn't we assume that the number of nurse hasn’t decreased ? How A is wrong?

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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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02 Jan 2020, 17:18
chowdhurysakib71 wrote:
GMATNinja wrote:
The author concludes that one of two things has happened over the past ten years: either 1) Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or 2) they are more sensitive to the chemicals than schoolchildren were ten years ago. How does the author arrive at this conclusion?

• We are given that exposure to cleaners and pesticides commonly used in schools can cause allergic reactions in some children.
• Over the past ten years, the proportion of schoolchildren sent to school nurses for allergic reactions to THOSE chemicals has increased significantly.

The author states two possible explanations for this increase, but are those the only options? The author's explanation will only hold up if one of the following is assumed:

Quote:
(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

A change to the number of nurses doesn't impact the number of students sent to see the nurses, so (A) can be eliminated.

But in A, the number of nurses matters? Because if the nurses number decrease, the proportion will be increase though after total number of students will not increase. So,shouldn't we assume that the number of nurse hasn’t decreased ? How A is wrong?

Posted from my mobile device

I'll steal a bit from this post that explains a similar issue with answer choice (E):

The author is trying to explain the proportion of elementary school students sent to nurses for treatment of allergic reactions:

• This proportion is a % of elementary school students.
• In a fraction, it would be expressed as [# of elementary students sent to the nurse for treatment of specific allergic reactions] / [total # of elementary students].

You can see that the number of nurses plays no role in the relevant proportion -- we only care about the number of students sent to the nurse for treatment as a proportion of the total number of students.

I hope that helps!
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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27 Feb 2020, 01:27
1
This is a classic question type of GMAT where they will present 2 reports. One from history and one from present and will generally ask us to find the assumption. Here the assumption generally lies in the fact that there are differences in the report.

Premise: There are more schoolchildren who are taken to school nurses than the number 10 years ago because of cleaners or pesticides.
Conclusion: Either Renston's schoolchildren have been exposed to greater quantities of the chemicals, or they are more sensitive to them than schoolchildren were ten years ago.

using the pre-thinking, the assumption can be:
There are more schoolchildren who are now being taken to the nurses now than they were taken 10 years ago. (This is the heart of such questions, a flaw in the previous report)

(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years. - Totally irrelevant
(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances. - The conclusion is not related to difference among substances
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago. - That's exactly what we thought in our prethinking
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston. - This kinda strengthen our argument but it doesn't involve any difference in report now and report 10 years ago.
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago. - This can also be a good strengthener and people might as well choose this as right answer but it is talking about proportion and our question is talking about absolute numbers

Hence the correct answer choice is (C)
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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06 Apr 2020, 03:57

Passage Analysis

• Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children.
o Exposure to some particular chemical substances causes allergic reactions in some children.
o These chemicals are commonly used in elementary schools as cleaners or pesticides.

• Elementary school nurses in Renston report that the proportion of schoolchildren sent to them for treatment of allergic reactions to those chemicals has increased significantly over the past ten years.
o Elementary school nurses in Renston have reported about the proportion of school children’s allergic reactions.
o The nurses state that over the last 10 years, the proportion of schoolchildren sent to treat allergic reactions to the abovesaid chemicals (as a fraction to the total population of school children) has risen by a significant number through the period.

• Therefore, either Renston's schoolchildren have been exposed to greater quantities of the chemicals, or they are more sensitive to them than schoolchildren were ten years ago.
o The author concludes that this phenomenon occurred because of either of the two possible reasons listed.
 One scenario is that the school children at Renston are exposed to higher amounts of the allergy causing chemicals.
 Another possibility is that the school children of Renston today are more likely to respond with allergic reaction to the same quantity of chemical exposure as the school children ten years ago were subjected to.

Conclusion: Either Renston's schoolchildren have been exposed to greater quantities of the chemicals, or they are more sensitive to them than schoolchildren were ten years ago.

Question Stem Analysis
We are required to identify the assumption needed to reach the conclusion of this argument.

Pre-thinking

Falsification Question
In what scenario is it possible that neither Renston's schoolchildren have been exposed to greater quantities of the chemicals, nor they are more sensitive to them than schoolchildren were ten years ago?
Given that
• Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children.
• Elementary school nurses in Renston report that the proportion of schoolchildren sent to them for treatment of allergic reactions to those chemicals has increased significantly over the past ten years.

Thought Process
The two possibilities listed by the author as reasons for the observed increase in the proportion of school children sent to be treated for allergies to the said chemicals are, either that the children today are exposed to more quantity of the chemicals, or that the children these days are more sensitive to the chemicals and prone to have allergic reactions triggered by lesser amounts of the same. The implicit assumption made by the author lies in the link between the actual number of school children who had allergic reactions and the number of schoolchildren sent to the nurses for this reason. An assumption has been made regarding the strength of the chemicals in question as well.

Falsification Condition#1
What if students were not sent to nurses for allergic reactions to the chemicals ten years ago as often as they are sent for the same reason now? In that case the facts hold but the conclusion breaks down.
Assumption#1
Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

Falsification Condition #2
What if, during the last ten years, the strength of the chemical used in the cleaners and pesticides has increased? In that case, neither of the two possibilities listed in the conclusion will be needed and the conclusion will break down.
Assumption#2
The strength of the chemical used in cleaners and pesticides has not increased during the last ten years.

(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.
INCORRECT
This option may confuse if the word ‘proportional’ in the passage is misunderstood as representing the ratio of schoolchildren sent for treatment to the number of nurses. But ‘proportional’ actually compares the allergic schoolchildren sent to be treated to the total population of school children. In this case, the number of school nurses makes no difference to the conclusion. Therefore, it is an incorrect answer.

(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.
INCORRECT
Allergies to other substances are totally out of context to our argument. Hence, this choice is an incorrect answer.

(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.
CORRECT
This information is necessary for the argument to hold and it is in line with our pre-thinking. Hence this is the correct answer choice.

(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.
INCORRECT
The usage of the chemicals in question anywhere outside elementary schools does not come under the purview of the argument, and hence, this option forms an incorrect choice.

(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.
INCORRECT
We are concerned only about the proportion of elementary school children sent to be treated for allergic reactions due to the mentioned chemicals as a ratio to the total number of elementary school children. The fraction the latter constitute among the total population of Renston is not a relevant factor in our analysis. Hence this is also a wrong answer choice.
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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08 Apr 2020, 07:17
The correct answer is option (C).

Understanding the passage:

1. Exposure to certain chemicals has caused allergies in school children
2. These chemicals are used as cleaners or pesticides in the elementary schools
3. In Renston, elementary school nurses say that - "the proportion of children sent to them for allergy treatment has increased significantly over the last 10 years"
4. Conclusion: Either 1) Renston's schoolchildren have been exposed to greater quantities of the chemicals (OR)
2) They are more sensitive to chemicals today than students from 10 years ago

Understanding the question
Find the assumption on which the argument depends.

Thought Process:

An assumption is that implicit thought which is not stated, but has to be true for the conclusion to hold true. So, if an assumption is not true (negated), then the conclusion should break. A failsafe way to identify the assumptions is to identify the conditions under which the conclusion would definitely break.

So, let us falsify or break the conclusion:

In what scenario - 1) (Neither) have Renston's schoolchildern been exposed to greater quantities of the chemicals
2) (Nor) are they more sensitive to chemicals today than students from 10 years ago

Given that 1) Exposure to these chemicals cause allergic reactions in school children 2) The proportion of students reporting to nurses for treatment of allergies due to these chemicals has increased.

Falsification Condition 1:
What if the concentration of the harmful component in these chemicals has increased, from ten years ago?
In such a case, even if the exposure level is the same as ten years ago (i.e. the amount of chemicals the children are exposed to is same), the amount of the harmful component of the chemical the children are exposed to will be more.

Example: 10 years ago, 50 grams of harmful component in 100 grams of chemical. Now, 75 grams of harmful component in every 100 grams of chemical. In terms of exposure to the chemical, the amount is still the same (say, 100 grams), but the exposure to the harmful component is higher (because of higher concentration (75 grams today instead of 50 grams 10 years ago)

Assumption 1: The concentration of the harmful component(s) in the chemicals has not increased today, as compared to 10 years ago

Falsification Condition 2:
What if students 10 years ago did not visit the nurse for allergies as often as students these days?
Maybe a significant number of students never visited the nurses for allergies, for whatever reason (maybe medicine those days was not good enough to justify going to a medic!). Then the increase in proportion observed is not because of the reasons mentioned in the conclusion, but because of this increased likelihood of visiting a nurse.

Assumption 2: Children who develop allergic reactions to the chemicals are not more likely to visit a nurse today, than they were 10 years ago

Let us look at the answer choices:

(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

Irrelevant. The conclusion is about schoolchildren visiting the nurses for allergies due to chemicals. The number of nurses has no relation to the conclusion.

(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

Irrelevant. The passage is specific to the chemicals used in cleaners/pesticides, which can cause allergies in school children. Any other substance has no impact on our conclusion, and cannot therefore, be the correct assumption.

(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

This is in line with our 2nd assumption. If children today are more likely to visit a nurse for allergies from these chemicals, then the increased proportion can be because of this increased likelihood rather than the points mentioned in the conclusion. Hence, this is the correct choice.

(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

Let us try negating this assumption. Even if these chemicals are commonly used as cleaners/pesticides in places other than elementary schools, that only means that the children may be exposed to even more quantities of the chemicals than previously assumed. This may be happening 10 years ago as well (if the same chemicals were used then too), but we do not know. In no way will this option break the conclusion.

(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

Irrelevant. The only relevant proportion in this argument is the proportion of students who went to nurses. The proportion of children in the population has zero impact on the conclusion.

Cheers!
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Re: Exposure to certain chemicals commonly used in elementary  [#permalink]

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22 May 2020, 05:54
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Re: Exposure to certain chemicals commonly used in elementary schools as  [#permalink]

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22 May 2020, 05:57
GMATNinja wrote:
The author concludes that one of two things has happened over the past ten years: either 1) Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or 2) they are more sensitive to the chemicals than schoolchildren were ten years ago. How does the author arrive at this conclusion?

• We are given that exposure to cleaners and pesticides commonly used in schools can cause allergic reactions in some children.
• Over the past ten years, the proportion of schoolchildren sent to school nurses for allergic reactions to THOSE chemicals has increased significantly.

The author states two possible explanations for this increase, but are those the only options? The author's explanation will only hold up if one of the following is assumed:

Quote:
(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

A change to the number of nurses doesn't impact the number of students sent to see the nurses, so (A) can be eliminated.

Quote:
(B) Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.

We are not concerned with allergies to other substances. Regardless of whether children allergic to the chemicals are more likely to have allergies to other substances, we still need to explain why more students are now sent to the nurses because of reactions to THOSE chemicals. The two theories in the conclusion are only meant to explain the increase in the number of schoolchildren sent to the nurses because of THOSE chemicals, so choice (B) is irrelevant.

Quote:
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.

According to the argument, the increase in the proportion of schoolchildren sent to the elementary school nurses is due to either greater exposure to the chemicals or a greater sensitivity to the chemicals. But what if children who have allergic reactions to the chemicals are more likely to be sent to a school nurse now than they were ten years ago? Maybe the amount and severity of the allergic reactions was the same ten years ago but students were simply less likely to be sent to the nurse back then. Maybe ten years ago the teachers simply let the suffering students remain in class with watery eyes and running noses (for example).

That could explain the increase in the proportion of schoolchildren sent to the elementary school nurses, even if students' exposure and sensitivity to the chemicals has not changed. In order for the argument to hold, the author must assume that children who have allergic reactions to the chemicals are NOT more likely to be sent to a school nurse now than they were ten years ago. Choice (C) looks good.

Quote:
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.

Perhaps the cleaners ARE commonly used in houses and apartments, but we don't care about WHERE the students were exposed to the chemicals. If exposure has increased, whether at school or at home, then the author's argument would be valid. The author does not say that exposure has increased AT THE SCHOOLS, so choice (D) can be eliminated.

Quote:
(E) Children attending elementary school do not make up a larger proportion of Renston's population now than they did ten years ago.

We are trying to explain an increase in the PROPORTION of students sent to the nurses, not an increase in the TOTAL NUMBER of students sent to the nurses. Thus, an increase in the number of students or the proportion of the population attending elementary schools does not matter. We need to explain the increase in the PROPORTION sent to the nurses for those allergic reactions. Choice (E) is not a required assumption and can be eliminated.

Choice (C) is the best answer.

(A) The number of school nurses employed by Renston's elementary schools has not decreased over the past ten years.

Doesn't that make much sense that a reduced number of nurses mean that each nurse will attend more children?
Suppose the number of nurses has been decreased to half, then each nurse will attend twice the number of children, thus they ended up reporting the "higher proportion" of schoolchildren being sent to them for the treatment.

Can you please tell me why my justification is flawed?
Re: Exposure to certain chemicals commonly used in elementary schools as   [#permalink] 22 May 2020, 05:57

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