Dental researchers recently discovered that tooth-brushes : GMAT Critical Reasoning (CR)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 16 Jan 2017, 11:45

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Dental researchers recently discovered that tooth-brushes

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 10 Mar 2008
Posts: 371
Followers: 5

Kudos [?]: 259 [0], given: 0

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

### Show Tags

18 Jul 2008, 01:18
4
This post was
BOOKMARKED
00:00

Difficulty:

15% (low)

Question Stats:

75% (02:26) correct 25% (01:32) wrong based on 934 sessions

### HideShow timer Statistics

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.
[Reveal] Spoiler: OA

Last edited by Narenn on 07 Oct 2013, 09:44, edited 3 times in total.
Necessary Corrections for Official Guide Verbal Review 2nd Edition Project
If you have any questions
New!
Magoosh GMAT Instructor
Joined: 28 Nov 2011
Posts: 307
Followers: 521

Kudos [?]: 982 [5] , given: 2

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

### Show Tags

23 Mar 2012, 11:14
5
KUDOS
Expert's post
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.
_________________

Christopher Lele
Magoosh Test Prep

Senior Manager
Joined: 14 Mar 2007
Posts: 317
Location: Hungary
Followers: 2

Kudos [?]: 25 [0], given: 3

### Show Tags

18 Jul 2008, 01:35
I think the answer is C. I am not 100% sure.
SVP
Joined: 28 Dec 2005
Posts: 1575
Followers: 3

Kudos [?]: 147 [0], given: 2

### Show Tags

18 Jul 2008, 03:53
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
SVP
Joined: 30 Apr 2008
Posts: 1887
Location: Oklahoma City
Schools: Hard Knocks
Followers: 40

Kudos [?]: 570 [0], given: 32

### Show Tags

18 Jul 2008, 05:14
E

vksunder wrote:
Dental researchers recently discovered that tooth-brushes can become contaminated wth 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.
Not knowing why doesn't attack the basis for the conclusion. It just means it happens, but we don't know why. No reason to think they're wrong.
(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.
Out of scope. It doesn't matter that they failed to investigate other contamination, the focus is on the contamination they DID find.
(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.
This is a close one, but in the end incorrect. The premise of the stem is all about the length of time the person uses the toothbrush. That is not mentioned at all here. It does weaken, but E weakens more because it undercuts the basic reason for the stem's conclusion.
(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.
Out of Scope. This has nothing to do the length of time the toothbrush is used. This has to do with a variable that changes from person to person. The length of use has to do with every toothbrush user. This doesn't weaken the stem.
(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 undercuts the premise of the stem by saying that after 6 weeks of use, there is no difference between toothbrushes. Sure their correlation worked after 4 weeks, but any variation was completely gone within 2 more weeks and their conclusion that we should toss the toothbrush after 4 weeks is invalid because it doesn't hold true after 6 weeks.

_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a.

GMAT Club Premium Membership - big benefits and savings

Manager
Joined: 28 Sep 2011
Posts: 206
GMAT 1: Q V
Followers: 1

Kudos [?]: 65 [0], given: 5

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

### Show Tags

23 Mar 2012, 09:57
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.
BSchool Forum Moderator
Joined: 23 Jul 2010
Posts: 574
GPA: 3.4
WE: General Management (Non-Profit and Government)
Followers: 106

Kudos [?]: 839 [0], given: 319

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

### Show Tags

31 Oct 2013, 02:00
Bumping for review and further discussion*.

Theory on Weaken the Argument Questions
Manhattan Gmat
Stacy Manhattan Gmat
Stacy Manhattan Gmat
Mangoosh GMAT
Knewton
e-gmat

Thursdays with Ron video sessions (Weaken and Strengthen questions)

Souvik's Article
Veritas prep

_________________

General Mistakes to Avoid on the GMAT
TOP 10 articles on Time Management on the GMAT
Thanks = Kudos. Kudos are appreciated

Rules for posting on the verbal forum

Manager
Status: Bouncing back from failure
Joined: 08 Mar 2010
Posts: 110
Schools: Wharton,MIT, Tepper, Kelly,
WE 1: 7 years- Service Managament, poject Management, Business Consultant- Retail
Followers: 1

Kudos [?]: 13 [0], given: 34

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

### Show Tags

03 Jul 2014, 05:56
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)

GMAT Club Legend
Joined: 01 Oct 2013
Posts: 10526
Followers: 917

Kudos [?]: 203 [0], given: 0

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

### Show Tags

14 Sep 2015, 04:34
Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
Intern
Joined: 15 Nov 2015
Posts: 48
Followers: 0

Kudos [?]: 4 [0], given: 1

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

### Show Tags

14 Apr 2016, 11:56
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.
Re: Dental researchers recently discovered that tooth-brushes   [#permalink] 14 Apr 2016, 11:56
Similar topics Replies Last post
Similar
Topics:
1 Researchers recently discovered an unusually high concentration of har 1 09 Jul 2015, 03:47
4 Recent dental research shows that bacteria around the gum 8 01 Oct 2012, 10:00
A medical research team in France recently discovered that 5 16 Jan 2012, 09:53
1 A psychobiologist recently discovered that gorillas that 11 14 May 2011, 00:19
3 Researchers have discovered that caffeine can be as 12 21 May 2010, 17:58
Display posts from previous: Sort by