#Some, #Proportion, #Argument Family

Question


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. 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.

Which of the following is an assumption on which the argument depends?

(Because of copyrights, the complete official question is not copied here. You can access the question here: GMAT Club)

Difficulty: Medium

Accuracy: 71%

Based on: 7750 sessions

Solution


The Story

Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children. – Elementary schools commonly use certain chemicals. Some children experience allergic reactions if exposed to such chemicals.

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. – Nurses in elementary schools in a particular town get schoolchildren sent to them for treatment of allergic reactions to those chemicals. The nurses report that the proportion of such schoolchildren they get has increased significantly over the past ten years.

(So, what exactly is the proportion that has gone up?
The proportion of schoolchildren who are sent to the nurses for treatment allergic reactions to those chemicals.
As a proportion of what?
Must be as a proportion of the total number of schoolchildren in elementary schools in Renston. I.e., total number of students sent to the nurses for the treatments as a fraction of the total number of schoolchildren. Something like, say earlier 10% of schoolchildren used to get sent to nurses, and now 30% of schoolchildren get sent.)

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. – The author concludes that one of two things must have happened:

  1. The exposure of schoolchildren to the chemicals has gone up
  2. Or, the children have become more sensitive to these chemicals

Author’s logic:
Since a higher proportion of children are sent to the nurses for treatment of allergic reactions to the chemicals (basis), either exposure or sensitivity has increased (main point).

Gap(s) in logic:
Maybe a similar proportion of students used to have allergic reactions, but teachers did not send them to nurses as frequently.

  • Possibly, they lacked awareness of the symptoms.
  • Or maybe they used to prescribe some basic medication themselves, but have since stopped. (Fear of lawsuits, possibly?)

Question Stem

Which of the following is an assumption on which the argument depends?

Framework:
The author assumes there can’t be any other reason apart from the one mentioned for why a higher proportion of such children are sent to the nurses.

Answer choice analysis


Answer Choice: A

Incorrect

Selected by: 7%

What if the number of school nurses employed by the schools has decreased over the past ten years (negation)?
Even then, the argument still remains valid.
In fact, if despite fewer nurses a higher proportion of children were sent for such treatments, perhaps exposure or sensitivity had increased. So, the negation does not break down the logic of the argument.


Answer Choice: B

Incorrect

Selected by: 5%

Step 1: What does the option mean?
Two groups of children are compared: those who are allergic to the discussed chemicals and those who are not.
What about these groups?
Group 1 is not more likely to be allergic to other things.
In other words, group 1 is equally or less likely to be allergic to other substances.
Now, Is there an assumption in the argument? The argument is about the treatment of, exposure to and sensitivity to certain specific types of chemicals. How children react to other chemicals or substances, and whether the reaction varies are irrelevant to the argument.


Answer Choice: C

Correct

Selected by: 71%

Statement: The likelihood of sending such children to a nurse has not increased in the ten years.
This one is in line with our initial understanding. The statement supports the argument.
And, if such children are more likely to be sent to nurses now than they were ten years ago (negation) then the argument breaks down. In that case, to still conclude that the reason must be either exposure or sensitivity doesn’t make sense.
The basis for the conclusion was the fact that a higher proportion of children are sent to the nurses for allergy treatments. And if the chances of sending such children had increased, then increased exposure or sensitivity would not be the reason.


Answer Choice: D

Incorrect

Selected by: 10%

Doesn’t matter. Whether these chemicals are used in houses is irrelevant. The conclusion is pretty broad in this regard. It mentions ‘exposed to greater quantities of the chemicals’. The conclusion does not discuss ‘where’ children get exposed.
So, even if the chemicals are commonly used as cleanness in houses (negation), the argument still remains valid.


Answer Choice: E

Incorrect

Selected by: 7%

Proportion of the town’s population = #  of children at the school / population of the town
Whether this proportion has changed, and if it has, in which direction are immaterial to the argument. Even if the children now make up a larger proportion (negation), the argument is not impacted.

If you have any doubts regarding any part of this solution, please feel free to ask in the comments section.


Anish Passi

GMAT Coach

With over a decade of GMAT training experience, top 1 percentile scores on the CAT and GMAT, and a passion for teaching, I’d like to believe I am quite qualified to be a GMAT coach. GMAT is learnable, and I help students master the GMAT through a process-oriented approach based on logic and common sense. I offer private tutoring and live-online classroom courses. My sessions are often sprinkled with real-world examples, references to movies, and jokes that only I find funny. You’ve been warned 🙂

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