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In the late 1980’s, the population of sea otters in the North Pacific

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In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 24 Jul 2010, 16:58
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In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline—increased predation by killer whales or disease—disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably

Which of the following, if true, most seriously weakens the reasoning?

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.

(B) There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.

(C) Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.

(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.

(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters

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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 25 Jul 2010, 08:56
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I was between A and C --- but realized later that C talks about 1980's as a whole whereas the population decline concerns late 80's. What put me off about A was the fact that just because killer whales seek "other" prey does not necessarily strengthen the conclusion that the whales killed the otters...but well oh well...A is the best of the available lot.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 25 Jul 2010, 09:08
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B - states that reason for decline of sea otters is not the migration to other location. But this doesn't weaken or streanthen the reason.

C - states that in 1980's population of sea otters decliend but no reason is stated for it.

D - states the affect of decline of sea otters. But this doesn't weaken or streanthen the reason.

E - Again just tells about population spread but nothing else which will weaken or streanthen the reason.

But A points out that possible reason for declie eof sea otters if whales started to kill them. So think A is the orrect choice.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 25 Jul 2010, 11:33
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Conclusion - disease more likely the cause for population decline of sea otters
Premise- seals and sea lions population has come down but whale population is not affected.

Choice A clearly states that killer whales could be the cause of decline as they turn out to sea otters when there is a decline in seals and sea lions population.

Other choices IMO strengthens the arg.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 26 Jul 2010, 12:03
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A for me as it points out that pollution was possibly not the reason for the decline in sea otters population. Thus weakening the reasoning.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 26 Jul 2010, 19:50
Only A gives an alternate explanation.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 26 Jul 2010, 21:17
A weakens the argument by saying decrease is due to killer whales not pollution.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 27 Jul 2010, 03:09
the author is citing Disease as a most possible reason for the decline in popullation of sea otters. This is a simple causal flaw argument and an alternale cause can break the argument. There4 A it is.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 27 Jul 2010, 03:40
A
gives a reason for decline is due to whales and not due to disease
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 27 Jul 2010, 12:25
A...........

but couldn't use my brain faced a similar question in Knewton ..... only word changes..... free test .got it wrong and remember the answer..........so just got it
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 27 Jul 2010, 14:00
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-- Conclusion is - diseases have caused sharp decline in sea otters. To weaken the argument, we need to find a reason other than the disease for sharp decline.

A. Killer whales in the North Pacific usually prey on seals and sea lions but will,
when this food source is scarce, seek out other prey.
-- Since killer whales had started preying on sea animals other than seals and sea lions, sea otters were the possible next option to them. Hence sea otters started declining in 1980's because killer whales started preying them. Hence A is correct answer choice.

B. There is no indication that substantial numbers of sea otters migrated to other
locations from the North Pacific in the 1980’s.
--Since there is no indication that sea otters migrated to location other than North Pacific, the possible cause of decline in not clear from this answer choice. Hence B cannot be a correct answer choice.

C. Along the Pacific coast of North America in the 1980’s, sea otters were absent
from many locations where they had been relatively common in former times.
-- Irrelevant. Hence cannot be a correct answer choice.

D. Following the decline in the population of the sea otters, there was an increase
in the population of sea urchins, which are sea otters’ main food source.
--This answer choice mentions decline in sea otters, however fails to mention the possible cause for it. Hence it cannot weaken the argument and cannot be a correct answer choice.

E. The North Pacific populations of seals and sea lions cover a wider geographic
area than does the population of sea otters
-- Irrelevant. Hence E cannot be a correct answer choice.
Thank You.


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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 07 Sep 2010, 03:16
After reading A you don't even have to look ahead...but good to see a different type of question.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 08 Sep 2010, 21:51
Premise : The number of sea otters has declined.
Premise: The sea lions and seals are affected by pollution related disease

Conclusion: Otters are also affected by the disease and that's the reason of decline in numbers

A states that as there is scarcity of sea lions and seals, the whales are preying the otters.

which weakens the reasoning.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 05 Nov 2010, 14:31
A is the only one which closely weakens the QS.

In C...it can be talking about another region around Pacific coast.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 11 Nov 2010, 12:29
Hi i disagree with option (a). It states that whales would usually eat the seals, but when this source gets scarce they move to other sources - we can not assume that they'll eat otters.

The otters' population might actually be affected by pollution like the seals and this argument does not weaken that. "Other sources" may or may not be otters.
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 06 Aug 2012, 21:24
Can anyone tell me vvhat is the conclusion of this argument

vvhat are vve trying to vveaken here could not follovv please

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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 31 Jul 2014, 02:18
it is good question indeed, struck between a and C , took a time and then realize

Killer whales in the North Pacific usually prey on seals and sea lions but will,
when this food source is scarce, seek out other prey.--->had killer whales eaten them they would have got infected by disease and would have died , there number does not decrease So A
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 12 Oct 2015, 06:47
noboru wrote:
In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline—increased predation by killer whales or disease—disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably

Which of the following, if true, most seriously weakens the reasoning?

A. Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
B. There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.
C. Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.
D. Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.
E. The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters



hi EMPOWERgmatMax

could you please provide your comments on this. I was between option A and C. I want to know how A is preferable over C?

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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 27 Apr 2017, 00:24
noboru wrote:
In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline—increased predation by killer whales or disease—disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably

Which of the following, if true, most seriously weakens the reasoning?

A. Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
B. There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.
C. Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.
D. Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.
E. The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters



Premises:
Population of sea otters is declining.
Two possible reasons: killer whales and disease.
Disease is more likely because disease is killing seals and sea lions and because killer whale population has remained steady.

The reasoning uses two prong logic to show why disease is more probable than killer whales:
Disease is already killing other animals so it could have spread to sea otters too.
The population of killer whales has remained steady.

We can weaken the conclusion by weakening either.

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.

This shows that even though the population of killer whales hasn't increased, they could be the reason for decreased sea otter population. Their usual prey - seals and sea lions - have dwindled because of disease. So they could be seeking out sea otters. Hence it weakens the argument by showing that even if the killer whale population has not increased, more of them could be relying on sea otters as food source.


(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.

Note that the scope of our argument is limited - out of two plausible explanations, one is more likely than the other. We don't have to worry about any other explanation. It is either disease or killer whales. We need to compare the likelihood of these two only. Hence any option talking about any other reasoning is out of scope of the argument.

(C) Along the Pacific coast of North America in the 1980s, sea otters were absent from many locations where they had been relatively common in former times.

This doesn't strengthen/weaken either of the two explanations. It just says that sea otter population has declined in a way that they are absent from some location. What caused it, disease or killer whales, we don't know.


(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters' main food source.

Again, this has nothing to do with WHY sea otter population declined - the concern of our argument. What happened after sea otter population declined is out of scope.

(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.

The geographical area covered by seals and sea lions doesn't affect our argument. We want to compare the two explanations - disease or killer whales. It doesn't affect either.
Note that a change in geographical area covered by prey of killer whales could have had some impact.

Answer (A)
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Re: In the late 1980’s, the population of sea otters in the North Pacific  [#permalink]

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New post 14 Jul 2017, 06:53
In the late 1980s, the population of sea otters in the North Pacific began to decline. There are two plausible explanations for the decline: predation, possibly by killer whales, or disease. Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

Which of the following, if true, most seriously weakens the reasoning?

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
Correct Answer.

(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.
This option is actually trying to eliminate a possible weakener. So not correct.

(C) Along the Pacific coast of North America in the 1980s, sea otters were absent from many locations where they had been relatively common in former times.
This option is irrelevant as we are concerned with whatever available population of sea otter in the late 1980s.

(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters' main food source.
Of course, this is ought to happen. But we not concerned about the aftermath of the decline in population of sea otters.

(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.
Again, irrelevant. We are worried about the population of the otters in the north pacific sea and not the coverage they had.
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Re: In the late 1980’s, the population of sea otters in the North Pacific   [#permalink] 14 Jul 2017, 06:53

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