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Dental researchers recently discovered that tooth-brushes can become

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Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post Updated on: 08 Apr 2019, 03:43
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Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

Which of the following, if true, would most weaken the conclusion above?


(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.

(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present.


Official Guide for GMAT Verbal Review, 2nd Edition

Practice Question
Question No.: 41
Page: 132
Difficulty:

Originally posted by vksunder on 18 Jul 2008, 02:18.
Last edited by Bunuel on 08 Apr 2019, 03:43, edited 4 times in total.
Necessary Corrections for Official Guide Verbal Review 2nd Edition Project
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 23 Mar 2012, 12:14
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Conclusion: People should throw away their toothbrushes after only four weeks of use.

Reasoning: In that time, enough bacteria has accumulated to cause strep throat and pneumonia.

To WEAKEN this argument we will need an answer choice that suggests we should not dispose of our 4-week old toothbrushes.

It seems that debate here is between (C) and (E), so I will focus on these two answer choices.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacteria that
cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who
used uncontaminated toothbrushes.


Contaminated toothbrushes, i.e. those brushes with bacteria, are no more likely to cause strep throat than non-contaminated toothbrushes. Therefore, one should not throw away their 4-week old toothbrushes. ANSWER.


(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not
correlate with a higher number of bacterial being present.

Let's say I have a contaminated 4-week old toothbrush, on which a small colony bacteria has grown. If I do not throw the toothbrush away, I am likely to get strep throat. Nevertheless, I continue using the toothbrush for another two weeks. Now at week 6 the colony of bacteria is still there. According to answer (E) the colony has not grown (greater length of use of a toothbrush did not correlate...)

Of course I should still throw the toothbrush away because it is contaminated. Remember, we have to find an answer choice that suggests that it makes no sense throwing our toothbrush away. (E) however suggests that we should still throw the toothbrush away at week 6, regardless of whether it is less contaminated than it was at week 4.
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 18 Jul 2008, 04:53
i am also leaning towards C. The researches are saying to replace the tootbrush once a month in order to avoid being affected by the viruses ... to weaken, we are basically saying that regardless of whether brush is replaced or not, rate of getting the virus is the same
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 23 Mar 2012, 10:57
I have chosen the answer C for this question:

The underlying assumption in the passage is that contamination with bacteria can cause illness among individuals. Therefore, we should be switching toothbrushes once a month to avoid this.

A. The fact that dental researchers could not discover why contamination happens does not matter because the contamination still happens and can cause illness. Therefore, individuals should still replace their toothbrushes. This answer choice does not weaken the argument.

B. This is irrelevant - we do not care that dental researchers did not investigate other types of contamination.

C. This is the correct answer. If individuals who use toothbrushes that are contaminated do not get any sicker than individuals who use uncontaminated toothbrushes, then changing the toothbrush every month is unnecessary.

D. This somewhat supports the argument because careful cleaning of the toothbrush does nothing to eliminate the contamination, so people should be continually changing toothbrushes.

E. The fact that the amount of bacteria did not increase does not weaken the argument. The reason is because there is still a certain amount of bacteria on the toothbrush that could cause illness to individuals.
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 03 Jul 2014, 06:56
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vksunder wrote:
Official Guide for GMAT Verbal Review, 2nd Edition

Practice Question
Question No.: 41
Page: 132
Difficulty:


Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

Which of the following, if true, would most weaken the conclusion above?

(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.

(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present.


This is a good causal problem

Contaminated brush (X) caused pneumonia and step throat (Y) . One way to weaken the causal issue is

Even if cause does occurs effect occurs (No X ---> still Y)
Ans C says that even uncontaminated brush cased pneumonia and step throat (Y)

Therefore C is clear answer
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 14 Apr 2016, 12:56
Conclusion: people should replace toothbrush at least once a month
Premise: Toothbrush gets contaminated with bacteria after 4 weeks of use.

Assumption: bacterial is more likely to cause illness

answer choice will undermine this assumption

Alternatively: Negate conclusion and select answer choice that supports the negated conclusion along with the premise.
Negated Conclusion: people should not replace toothbrush at least in a month.
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 19 Jan 2017, 12:01
Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

Type - weaken
Boil it down - Contamination of toothbrushes occur after four weeks of usage and hence people should replace their toothbrushes once a month.
Pre-thinking - to weaken this we need an option that tells that probability that people will contract pneumonia and strep throat is minimal even after first four weeks

(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks. - Irrelevant - reason is not important

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms. - Out of scope

(C) The dental researchers found that among people who used toothbrushes contaminated with bacteria that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes. - Correct - If this is true then there is no point replacing the toothbrush every 4 weeks

(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use. -Irrelevant

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present. - Incorrect - what about the period of time from 4 weeks to 6 weeks .

Answer C
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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New post 25 Jul 2018, 02:56
Question Que: "weaken the conclusion"
Question Type: weaken, argument

To weaken this type of question:
1. find conclusion 2.find evidence (premise) 3.find assumption (gap) 4. ATTACK the gap (alternate cause)

Conclusion: Replace contaminated toothbursh after a month
(Scope change)
Evidence: Used Tooth brush after a month are contaminated with bac p and s

Assumption (pre-thinking that closes the gap):
If Use Contaminated toothbursh, then will be infected with P and S, therefore must throw toothbursh

Weaken:
Using contaminated toothbursh might not get infected with P and S. It might be Other reason that cause the infection.

Answer Choice C:
The incedence of diseases using contaminated and non contaminated are the same. (Might something else that causes the infection)
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Re: Dental researchers recently discovered that tooth-brushes can become  [#permalink]

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Re: Dental researchers recently discovered that tooth-brushes can become   [#permalink] 26 Aug 2019, 06:39
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