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# Lyme disease is caused by a bacterium transmitted to humans

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Joined: 01 Jan 2012
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Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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31 Mar 2012, 10:32
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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that

[Reveal] Spoiler:
Why option B is wrong
[Reveal] Spoiler: OA
If you have any questions
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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19 Mar 2013, 21:57
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This is a very interesting and somewhat tricky question. Here is my analysis of this question.

Bacteria -> whitefooted mice -> larvae of deer ticks -> humans
Larvae also feed on 'other species' which do not harbor the bacterium.

Conclusion: Increase the population of 'other species'; fewer people will get Lyme disease.

Strengthen the conclusion:

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.

Out of scope.

B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.

Out of scope. Argument doesn't discuss whether humans can directly contract Lyme disease. The argument only deals with Lyme disease through deer ticks. Let me elaborate on this. Say 100 people contract Lyme disease every year. At least some of them are through infected deer ticks. If number of infected deer ticks is reduced, the number of infected humans will reduce too. It is immaterial whether there are other ways of contracting lyme disease. If all 100 humans get infected through deer ticks, the number of infected humans might go down to 50. If half get infected directly and half through deer ticks, number of infected humans may go down to 75. In any case, we do expect the number of humans infected to go down. Hence, we can say that option (B) has no relevance as far as our conclusion goes. We are only concluding that there will be a decrease - not the amount of decrease.

C. A deer tick feeds only once while in the larval stage.
If there are more uninfected food sources, it is likely that when the larvae feed, they feed on uninfected food. If the larvae do not feed again, it is probable that they will not carry the bacterium of Lyme disease and hence fewer humans will get affected. Answer (C)

D. A single host animal can be the source of bacteria for many tick larvae.
It doesn't strengthen our plan since bacteria could still proliferate if a single host can be source for many tick larvae. So we may not see much decrease in Lyme disease in humans.

E. None of the other species on which deer tick larvae feed harbor other bacteria that
ticks transmit to humans.

Out of scope.
_________________

Karishma
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Current Student Joined: 28 Apr 2012 Posts: 306 Location: India Concentration: Finance, Technology GMAT 1: 650 Q48 V31 GMAT 2: 770 Q50 V47 WE: Information Technology (Computer Software) Followers: 29 Kudos [?]: 410 [2] , given: 142 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Feb 2013, 00:07 2 This post received KUDOS X disease -> to humans -> from deer ticks. larva deer ticks -> from feeding white footed mice (culprit) Other food sources of "deer ticks" do not cause infection. So if other food sources are increased, "deer ticks" would feed on them and refrain from feeding white footed mice. What if, deer tick larva feeds both on white footed mice and alternative source ? My conclusion won't be valid in that case. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. I am not bothered about suffering if ticks B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. Does not help. Number of white-footed mice remain same before/after increased other food sources for larvae. Humans would be benefited by decreased infected ticks. C. A deer tick feeds only once while in the larval stage. If deer ticks feed only once in larval stage and they have abundant infect free sources, then there will be less infected ticks and our conclusion that humans will be safer holds valid. D. A single host animal can be the source of bacteria for many tick larvae. That is possible, but we are not concerned on number of mice. If alternative food sources are availble, atleast some ticks would be non-infected. E. None of the other species on which deer tick larvae feed harbor other bacteria already clarified in the premise, " certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species " _________________ "Appreciation is a wonderful thing. It makes what is excellent in others belong to us as well." ― Voltaire Press Kudos, if I have helped. Thanks! e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [1] , given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 25 Feb 2013, 23:08 1 This post received KUDOS Expert's post monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, I'll just focus on your question that why B is incorrect. Let's first identify the conclusion: Conclusion: if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. So, this is a causal argument i.e. an argument which says that if you do X, you'll achieve Y. In this specific case, it says IF population of these other species were increased (X), then, 1. the number of ticks acquiring the bacterium would likely decline(Y) 2. and hence the number of people contracting Lyme disease would likely decline (Z) A strengthener is a statement which increases our belief in the conclusion. Let's look at option B to find out if it does so. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. It means that humans cannot directly acquire Lyme disease through white-footed mouse. But how does it affect the conclusion? If one of the ways of acquiring a disease is reduced, it should lead to a "decline" in the incidence of disease, irrespective of the fact that there are other ways to acquire a disease. For example: If a disease X can be acquired through two mediums: A and B. If I decrease A, then it should lead to a decline in X, irrespective of the fact that there are other ways to acquire the disease. However, there is a catch. If the conclusion had stated that the disease will be eliminated, then in that case I would need to consider whether there are other ways to acquire the disease or not. Hope this helps Let me know if you have any further queries. Thanks, Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [1] , given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 20 Mar 2013, 23:57 1 This post received KUDOS Expert's post 1 This post was BOOKMARKED monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, Here is the detailed analysis of this question. Understanding the Passage Premises: 1. Lyme disease is caused in humans by DT (Deer Ticks) 2. DT pick up the bacteria in the larva stage by feeding on infected WFM (White Footed Mice) 3. DT also eats other species which don't have bacteria So, (conclusion) if we increase these OS (other species), the number of DT with bacteria will reduce and this will lead to reduction in the number of incidence of disease in humans. Can you understand how the conclusion is drawn? Let's understand it. DT eats OS and WFM. For illustration, let's suppose there are 50 OS and 50 WFM. In such a scenario, the probability of a DT eating WFM is 50%. Now, suppose we increase the number of OS to 450, then we have total of 500 eatables out of which only 10% are WFM, so now the probability of DT eating WFM has come down to 10%. Therefore, if we increase OS without increasing WFM, the number of DT acquiring bacteria should reduce. This is the conclusion. Prethinking Here, let's think of an assumption built in the above conclusion. It's a bit difficult if you are not very comfortable with random events and probabilities. The assumption is that DT does not have a preference of eating WFM over OS because if DT does have a preference, then even if we increase OS, DT will still eat WFM as long as WFM exists. Thus, for our conclusion to hold, this assumption is required. For people familiar with random events and probability, read this; other can skip directly to Analysis of Option statements Look at the example we took above in which we said that increasing OS to 450 and keeping WFM at 50 will make the probability of eating WFM 10%. This is based on the assumption that eating by DT is a random event or in other words, DT eats randomly whatever is lying in front of it. If we keep more OS, then the probability of eating OS will increase. However, if eating by DT is not a random event and is rather skewed towards certain possibilities, then increasing OS might not help. Analysis of option statements Before marching on, remember that we are here to find a strengthener to the conclusion that increase OS will lead to lesser DT acquring bacteria and eventually lesser humans acquiring the disease A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. - Whether they suffer or not, it doesn't matter. They make us (humans) suffer. Not relevant. Incorrect. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. - This option indicates that humans don't acquire Lyme disease directly from WFM. Let’s take the opposite and say that humans could contract Lyme disease from WFM. Now, when we increase OS, then DT will eat less of WFM. This will lead to an increase in WFM numbers. Since humans can acquire the disease directly through WFM, it would lead to increase in incidence of Lyme disease in humans. This creates doubt about the conclusion. So, this option, by indicating that humans don't acquire the disease through WFM, eliminates the doubt and hence, should be a strengthener. But there is a catch – a flaw in the above reasoning. The truth is that DT don't kill WFM and then eat them. DT are very small insects - they can't really kill mice. Like a mosquito doesn't need to kill us to feed on us. So, even if DT feeds less on WFM, it won’t lead to an increase in the numbers of WFM. Therefore, population of WFM doesn’t change on the implementation of the plan. Therefore, whether human can acquire Lyme disease directly through WFM doesn't affect the conclusion. Incorrect C. A deer tick feeds only once while in the larval stage. – This requires some understanding. Consider two scenarios: 1. Deer tick feeds only once 2. Deer tick feeds 20 times First scenario: Deer tick feeds only once Suppose we have 80 OS and 20 WFM. What is the probability of deer tick getting the bacteria? Simple. Probability = 0.2 (i.e. same as proportion of WFM) Second scenario: Deer ticks feeds 20 times. What is the probability of deer tick getting the bacteria? Remember that DT gets the bacteria even if it feeds on WFM for only once out of 20 times. So, we can say that Probability = 1 – P (DT not feeding on WFM even once) = 1 – (0.8)^20 = 1 – 0.11 = 0.89 So, what do we see? If DT eats more number of times, then even with the same proportion of OS and WFM, more DT gets bacteria. Therefore, when DT eats only once, reducing the number of WFM will have the most impact in terms of reducing the number of infected DT. Therefore, this option strengthens the conclusion. Correct. D. A single host animal can be the source of bacteria for many tick larvae. – This is fine but this will apply to both OS and WFM. If it applied to only OS, then it would strengthen our case like Option C. But since it applies to both, it doesn't impact the conclusion. Incorrect. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans – We are only concerned about bacteria related to Lyme disease. This doesn't affect the conclusion. Incorrect. Hope this helps Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com Retired Moderator Status: 2000 posts! I don't know whether I should feel great or sad about it! LOL Joined: 04 Oct 2009 Posts: 1672 Location: Peru Schools: Harvard, Stanford, Wharton, MIT & HKS (Government) WE 1: Economic research WE 2: Banking WE 3: Government: Foreign Trade and SMEs Followers: 103 Kudos [?]: 992 [0], given: 109 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 31 Mar 2012, 18:56 +1 C If the larvae feeds in a non infected species, it won't have the chance of feeding on an infected one later. _________________ "Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can." My Integrated Reasoning Logbook / Diary: http://gmatclub.com/forum/my-ir-logbook-diary-133264.html GMAT Club Premium Membership - big benefits and savings Current Student Joined: 30 Apr 2011 Posts: 15 Followers: 0 Kudos [?]: 4 [0], given: 0 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 01 Apr 2012, 14:27 metallicafan wrote: +1 C If the larvae feeds in a non infected species, it won't have the chance of feeding on an infected one later. I guess my question is how do you know they will eat the other species first? Can you elaborate on your answer? On the other hand, if you know that there no other ways to get the disease then the argument strengthens that the number of people acquiring the disease from ticks exclusively would decrease. Manager Status: Bunuel's fan! Joined: 08 Jul 2011 Posts: 233 Followers: 1 Kudos [?]: 47 [0], given: 55 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 29 Apr 2012, 11:03 This choice is incomplete. This kinda throw me off. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans. Also this is a gmat prep question. Director Joined: 03 Aug 2012 Posts: 896 Concentration: General Management, General Management GMAT 1: 630 Q47 V29 GMAT 2: 680 Q50 V32 GPA: 3.7 WE: Information Technology (Investment Banking) Followers: 24 Kudos [?]: 765 [0], given: 322 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 23 Feb 2013, 22:13 Someone please throw some light upon this one. Rgds, SA _________________ Rgds, TGC! _____________________________________________________________________ I Assisted You => KUDOS Please _____________________________________________________________________________ Senior Manager Joined: 22 Nov 2010 Posts: 285 Location: India GMAT 1: 670 Q49 V33 WE: Consulting (Telecommunications) Followers: 5 Kudos [?]: 157 [0], given: 75 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Feb 2013, 00:16 Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. [CONCLUSION] Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. OFS B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. No effect on conclusion. Although , it tries to eliminate one of the other source of disease C. A deer tick feeds only once while in the larval stage. CORRECT D. A single host animal can be the source of bacteria for many tick larvae. OFS. E. None of the other species on which deer tick larvae feed harbor other bacteria that Please provide complete option Cause & Effect: deer ticks ---feeds on infected food in the larval stage---> Lyme disease. Passage proposes to increase the number of UN-infected feeds to reduce the spread of Lyme disease. Now suppose, there are 10 infected feeds & 10 UN-infected feeds. And as per plan we increase the UN-infected feeds to 100. But if a larva feeds multiple times than even after having UN-infected feeds for 6 time (for e.g.), it haves infected feed than it will carry the bacterium that causes Lyme disease. Therefore, choice C strengthens the conclusion BY RESTRICTING THE NO. OF FEEDS IN THE LARVAL STAGE _________________ YOU CAN, IF YOU THINK YOU CAN BSchool Forum Moderator Joined: 27 Aug 2012 Posts: 1194 Followers: 134 Kudos [?]: 1615 [0], given: 144 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 02 Mar 2013, 04:16 Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. _________________ e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [0], given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 02 Mar 2013, 10:03 debayan222 wrote: Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. Hi Debayan, Interesting doubt! Before I respond to this, can you please tell me why you think option C is correct? This would help me understand the exact source of your doubt. Thanks, Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com BSchool Forum Moderator Joined: 27 Aug 2012 Posts: 1194 Followers: 134 Kudos [?]: 1615 [0], given: 144 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 19 Mar 2013, 11:54 egmat wrote: debayan222 wrote: Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. Hi Debayan, Interesting doubt! Before I respond to this, can you please tell me why you think option C is correct? This would help me understand the exact source of your doubt. Thanks, Chiranjeev Hey Chiranjeev, Sorry man for late come back...!Somehow I missed your reply and now have found it out while going through my inbox. Option C-as the feeding is only once on the active species so if the no. of inactive species is increased then the disease would likely decline. IMO-it turns out to be the best available option in this case. Awaiting your detail analysis! _________________ Manager Joined: 10 Jan 2010 Posts: 79 Schools: IIM Followers: 0 Kudos [?]: 26 [0], given: 11 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 21 Mar 2013, 10:40 egmat wrote: monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, Here is the detailed analysis of this question. Understanding the Passage Premises: 1. Lyme disease is caused in humans by DT (Deer Ticks) 2. DT pick up the bacteria in the larva stage by feeding on infected WFM (White Footed Mice) 3. DT also eats other species which don't have bacteria So, (conclusion) if we increase these OS (other species), the number of DT with bacteria will reduce and this will lead to reduction in the number of incidence of disease in humans. Can you understand how the conclusion is drawn? Let's understand it. DT eats OS and WFM. For illustration, let's suppose there are 50 OS and 50 WFM. In such a scenario, the probability of a DT eating WFM is 50%. Now, suppose we increase the number of OS to 450, then we have total of 500 eatables out of which only 10% are WFM, so now the probability of DT eating WFM has come down to 10%. Therefore, if we increase OS without increasing WFM, the number of DT acquiring bacteria should reduce. This is the conclusion. Prethinking Here, let's think of an assumption built in the above conclusion. It's a bit difficult if you are not very comfortable with random events and probabilities. The assumption is that DT does not have a preference of eating WFM over OS because if DT does have a preference, then even if we increase OS, DT will still eat WFM as long as WFM exists. Thus, for our conclusion to hold, this assumption is required. For people familiar with random events and probability, read this; other can skip directly to Analysis of Option statements Look at the example we took above in which we said that increasing OS to 450 and keeping WFM at 50 will make the probability of eating WFM 10%. This is based on the assumption that eating by DT is a random event or in other words, DT eats randomly whatever is lying in front of it. If we keep more OS, then the probability of eating OS will increase. However, if eating by DT is not a random event and is rather skewed towards certain possibilities, then increasing OS might not help. Analysis of option statements Before marching on, remember that we are here to find a strengthener to the conclusion that increase OS will lead to lesser DT acquring bacteria and eventually lesser humans acquiring the disease A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. - Whether they suffer or not, it doesn't matter. They make us (humans) suffer. Not relevant. Incorrect. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. - This option indicates that humans don't acquire Lyme disease directly from WFM. Let’s take the opposite and say that humans could contract Lyme disease from WFM. Now, when we increase OS, then DT will eat less of WFM. This will lead to an increase in WFM numbers. Since humans can acquire the disease directly through WFM, it would lead to increase in incidence of Lyme disease in humans. This creates doubt about the conclusion. So, this option, by indicating that humans don't acquire the disease through WFM, eliminates the doubt and hence, should be a strengthener. But there is a catch – a flaw in the above reasoning. The truth is that DT don't kill WFM and then eat them. DT are very small insects - they can't really kill mice. Like a mosquito doesn't need to kill us to feed on us. So, even if DT feeds less on WFM, it won’t lead to an increase in the numbers of WFM. Therefore, population of WFM doesn’t change on the implementation of the plan. Therefore, whether human can acquire Lyme disease directly through WFM doesn't affect the conclusion. Incorrect C. A deer tick feeds only once while in the larval stage. – This requires some understanding. Consider two scenarios: 1. Deer tick feeds only once 2. Deer tick feeds 20 times First scenario: Deer tick feeds only once Suppose we have 80 OS and 20 WFM. What is the probability of deer tick getting the bacteria? Simple. Probability = 0.2 (i.e. same as proportion of WFM) Second scenario: Deer ticks feeds 20 times. What is the probability of deer tick getting the bacteria? Remember that DT gets the bacteria even if it feeds on WFM for only once out of 20 times. So, we can say that Probability = 1 – P (DT not feeding on WFM even once) = 1 – (0.8)^20 = 1 – 0.11 = 0.89 So, what do we see? If DT eats more number of times, then even with the same proportion of OS and WFM, more DT gets bacteria. Therefore, when DT eats only once, reducing the number of WFM will have the most impact in terms of reducing the number of infected DT. Therefore, this option strengthens the conclusion. Correct. D. A single host animal can be the source of bacteria for many tick larvae. – This is fine but this will apply to both OS and WFM. If it applied to only OS, then it would strengthen our case like Option C. But since it applies to both, it doesn't impact the conclusion. Incorrect. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans – We are only concerned about bacteria related to Lyme disease. This doesn't affect the conclusion. Incorrect. Hope this helps Chiranjeev Very nice explanation, Chiranjeev. Thanks Manager Joined: 07 Feb 2011 Posts: 103 Followers: 0 Kudos [?]: 60 [0], given: 45 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Mar 2013, 04:01 VeritasPrepKarishma wrote: This is a very interesting and somewhat tricky question. Here is my analysis of this question. Bacteria -> whitefooted mice -> larvae of deer ticks -> humans Larvae also feed on 'other species' which do not harbor the bacterium. Conclusion: Increase the population of 'other species'; fewer people will get Lyme disease. Strengthen the conclusion: A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. Out of scope. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. Out of scope. Argument doesn't discuss whether humans can directly contract Lyme disease. The argument only deals with Lyme disease through deer ticks. Let me elaborate on this. Say 100 people contract Lyme disease every year. At least some of them are through infected deer ticks. If number of infected deer ticks is reduced, the number of infected humans will reduce too. It is immaterial whether there are other ways of contracting lyme disease. If all 100 humans get infected through deer ticks, the number of infected humans might go down to 50. If half get infected directly and half through deer ticks, number of infected humans may go down to 75. In any case, we do expect the number of humans infected to go down. Hence, we can say that option (B) has no relevance as far as our conclusion goes. We are only concluding that there will be a decrease - not the amount of decrease. C. A deer tick feeds only once while in the larval stage. If there are more uninfected food sources, it is likely that when the larvae feed, they feed on uninfected food. If the larvae do not feed again, it is probable that they will not carry the bacterium of Lyme disease and hence fewer humans will get affected. Answer (C) D. A single host animal can be the source of bacteria for many tick larvae. It doesn't strengthen our plan since bacteria could still proliferate if a single host can be source for many tick larvae. So we may not see much decrease in Lyme disease in humans. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans. Out of scope. Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected. I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question _________________ We appreciate your kudos' Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7370 Location: Pune, India Followers: 2285 Kudos [?]: 15093 [0], given: 224 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Mar 2013, 20:54 manimgoindowndown wrote: Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected. I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question Actually, (B) is not even an assumption. It is out of scope and has nothing to do with our current argument. Even if 'infection by deer ticks' is just one of the ways of acquiring Lyme disease, if you decrease the number of infected deer ticks (by increasing population of other food sources), you will expect to decrease the number of infected humans. So whether there are other sources of Lyme disease infection, doesn't bother our argument at all. When will it make a difference? Consider the same argument with a different conclusion: Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline proportionally. This conclusion says that if you increase other food sources and hence, decrease the number of infected deer ticks by say 50%, number of people contracting lyme disease will decrease by 50% too. Here you are assuming that there is no other source of infection in humans and decrease in number of infected ticks might make you see proportional results. We are trying to quantify the decrease here and hence the other ways of getting infected come into play. In our original argument, all we are focusing on is that if you can control one way of getting infected, you will decrease the number of human infections. It may be the only way of getting infected or there may be other ways too. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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09 Apr 2013, 20:42
VeritasPrepKarishma wrote:
manimgoindowndown wrote:

Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected.

I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question

Actually, (B) is not even an assumption. It is out of scope and has nothing to do with our current argument. Even if 'infection by deer ticks' is just one of the ways of acquiring Lyme disease, if you decrease the number of infected deer ticks (by increasing population of other food sources), you will expect to decrease the number of infected humans. So whether there are other sources of Lyme disease infection, doesn't bother our argument at all.

So you're saying that B actually decreases the number of infected humans but doesn't adress the issue of infected dear ticks because the population of infected mice is still the same?

What you said in bold is what we are tryign to strengthen, no? That less humans are infected?
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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09 Apr 2013, 22:57
manimgoindowndown wrote:

So you're saying that B actually decreases the number of infected humans but doesn't adress the issue of infected dear ticks because the population of infected mice is still the same?

What you said in bold is what we are tryign to strengthen, no? That less humans are infected?

I am not sure from where you got this. (B) doesn't do anything to the number of infected humans. It only tells you that direct infection is not a source of infection in humans. That whoever gets it, doesn't get it by directly through white footed mice. It is immaterial really. All we need to focus on is the relation:

whitefooted mice -> deer ticks -> humans
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