Two types of earthworm, one black and one red-brown, inhabit : GMAT Critical Reasoning (CR)
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# Two types of earthworm, one black and one red-brown, inhabit

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Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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05 Jun 2013, 01:31
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Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.

B) The birds that prey on earthworms prefer black worms to red-brown worms.

C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

D) The average life span of the earthworms has remained the same since the factory began operations.

E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
[Reveal] Spoiler: OA

Last edited by Zarrolou on 05 Jun 2013, 01:33, edited 1 time in total.
Edited the question, renamed the topic.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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05 Jun 2013, 02:07
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Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.
Which of the following, if true, would most strengthen the conclusion of the local ecologists?
A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
B) The birds that prey on earthworms prefer black worms to red-brown worms.
C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
D) The average life span of the earthworms has remained the same since the factory began operations.
E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.[/quote]

I think you are confused because you didn't notice the conclusion carefully. Conclusion states that the population of black worms is equal to red-brown worms caused solely stemming from the blackening of the woods.

Two scenarios can happen-
1) Population of black worms increase while population of red-brown worms remains constant.
2) Population of black worms remains constant while population of red-brown worms decreases.
But no where it is mentioned which scenario actually happened. But the main point is that this change in population is entirely caused by blackening of the woods.

So this is basically Cause & Effect reasoning. In order to strengthen such type of reasoning, we have to prove that NO OTHER scenario can cause this relative change in population.

Option C states that climate was more favorable for red-brown worms than black worms. If this is to be taken as true, it refutes scenario 1.
What bout scenario 2.
Population of black worms remains constant while population of red-brown worms decreases. HOW
Even the climate is more favorable for red-brown worms, yet their population decreased because they lost Camouflage advantage as all the surroundings are turned black, they can be easily found & preyed. This proves that it was blackening of the woods that led to this change in relative population

Hope this helps
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Last edited by fameatop on 05 Jun 2013, 02:11, edited 2 times in total.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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05 Jun 2013, 02:08
srabani88 wrote:
Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.

B) The birds that prey on earthworms prefer black worms to red-brown worms.

C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

D) The average life span of the earthworms has remained the same since the factory began operations.

E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.

Since the evidence is "The population of black earthworms is now almost equal to that of the red-brown earthworm" , we need to find the choice which eliminates the possibility that the equality in population is not due to decline in population of red-brown earthworm.

Choice C does that.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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05 Jun 2013, 02:31
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Here are my 2 cents...

Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

I've highlighted the pieces separately to draw attention to the role each piece plays independently.

The word result, as we know, signals the conclusion. This can be deciphered even if you are the kind of person that does not read the question first.

If you have read the question before the passage you know that say local ecologists in the passage clearly correlates with the question, telling you exactly where the conclusion lies. You would be able to decipher this even if you missed the word result.

That said, the conclusion follows. Pay attention to the words; they say solely stemming from the blackening of the woods. This means there is no reason why red-brown earthworms would dwindle.

Now you need to find the choice that strengthens this idea, that is, while favoring both types of what could contribute to the rise in black earthworm population?

The former part of the passage already states that black earthworms could not be well disguised and hence often fell prey to predatory birds. So what could be helping their proliferation now? Blackening of the woods. What can strengthen this position? Eliminate the choices that suggest the red-brown earthworms are dwindling.

A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
This is a weakening idea. Plus it could go contrary to what the passage suggests.

B) The birds that prey on earthworms prefer black worms to red-brown worms.
This may be close, so I would keep it

C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
This option clearly strengthens the conclusion. Although I would say choice B goes with the tide, it does not to anything to strengthen the conclusion. Now we don't want a choice that simply states the lines in the passage again. This choice states that even though climatic conditions favored the red-brown worms, the black worms were able to proliferate. Why? Because the woods blackened and the birds were not able to prey on the worms.

D) The average life span of the earthworms has remained the same since the factory began operations.
E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Irrelevant choices.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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15 May 2014, 01:23
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petrifiedbutstanding wrote:
Here are my 2 cents...

Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

I've highlighted the pieces separately to draw attention to the role each piece plays independently.

The word result, as we know, signals the conclusion. This can be deciphered even if you are the kind of person that does not read the question first.

If you have read the question before the passage you know that say local ecologists in the passage clearly correlates with the question, telling you exactly where the conclusion lies. You would be able to decipher this even if you missed the word result.

That said, the conclusion follows. Pay attention to the words; they say solely stemming from the blackening of the woods. This means there is no reason why red-brown earthworms would dwindle.

Now you need to find the choice that strengthens this idea, that is, while favoring both types of what could contribute to the rise in black earthworm population?

The former part of the passage already states that black earthworms could not be well disguised and hence often fell prey to predatory birds. So what could be helping their proliferation now? Blackening of the woods. What can strengthen this position? Eliminate the choices that suggest the red-brown earthworms are dwindling.

A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
This is a weakening idea. Plus it could go contrary to what the passage suggests.

B) The birds that prey on earthworms prefer black worms to red-brown worms.
This may be close, so I would keep it

C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
This option clearly strengthens the conclusion. Although I would say choice B goes with the tide, it does not to anything to strengthen the conclusion. Now we don't want a choice that simply states the lines in the passage again. This choice states that even though climatic conditions favored the red-brown worms, the black worms were able to proliferate. Why? Because the woods blackened and the birds were not able to prey on the worms.

D) The average life span of the earthworms has remained the same since the factory began operations.
E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Irrelevant choices.

I am not sure if the option B) "it does not to anything to strengthen the conclusion". It actually does so. As the birds that prey earthworms prefer black to red,then also the population of black increases strengthens the ecologist idea that population has increased because of camouflage protection of black earthworms.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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05 Oct 2015, 11:29
quite amazing question :-

okay so i eliminated A as it seem to be a repetition of facts only ;

B- this might imply that if the birds preferred black then red might be depreciating because of something else

E- out of scope

main confusion was bw C and D -

atlast went with C as D forms general statement for both whereas C said even after favourable conditions red reduced to same number as black. so C

kudos to this question .....
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Re: Two types of earthworm, one black and one red-brown, inhabit   [#permalink] 05 Oct 2015, 11:29
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