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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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19 Jan 2013, 23:16
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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:
What is wrong with option (A)? As we have to prove that after factory operations the red ones were more visible than the black ones ,so this should provide support to "Black = Red solely stemming from the" blackening of the woods."
Knowing that factory operations was the cause of " blackening of the woods."
[Reveal] Spoiler: OA

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

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19 Apr 2013, 23:43
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Tough question. This is an example of the combination of CAUSES & EFFECTS and COMPARISON.

MAIN IDEA:

Before event A, X is less than Y.
After event A, X and Y are equal
Conclusion: Event A causes X increase.

Assumption: Y does not decrease itself or there's NO factors make Y decrease.

Negation to confirm: If Y decreases itself ==> cannot say Event A causes X increase (because X is the same, only Y decreases to make two variables are equal).

(A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
Wrong. Actually A weakens the conclusionn not strengthen because it says red-brown earthworms decreased by itself.

(B) The birds that prey on earthworms prefer black worms to red-brown worms.
Wrong.. Shell game. Birds prefer black worms ==> why birds prefer black worms, because birds can see black worms ==> if they cannot see black worms, how can they prefer them? ==> we can infer that the blackening of the woods does not play any role to help black worms.

(C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
Correct. C definitely says the number of red worms does not decrease, even red worms increased their population more than in 1980 ==> However, the number of black worms equals to that of red worms ==> the the blackening of the woods must play an important role to help black worms.

(D) The average life span of the earthworms has remained the same since the factory began operations.
Wrong.. D only says the AVERAGE life span of earthworms unchanged. Let analyze an example.

Before: The number of Red earthworms is five times that of Black earthworms. (100 vs 20)
There are 20 Black earthworms (BW), their life span is 11 days
There are 100 Red earthworms (RW), their life span is 5 days
Average life span = [20*11 + 100*5] / 120 = 6 days

After. The number of Red earthworms equals that of Black earthworms. (20 vs 20)
There are 20 BW, their life span is 11 days
There are 20 RW, their life span is 1 day (Let say, Emission from factory affected only RW, leading to RW reduced both its number and its life span. Blackening did not affect BW at all)
Average life span = [20*11 + 20*1] /40 = 6 days

(E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Wrong.. Apposite answer. Factory reduces emission ==> woods are less blacken ==> But the number of earthworm increase ==> the blackening of the woods does not play any role.

Hope it helps.
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Last edited by pqhai on 20 Apr 2013, 11:57, edited 4 times in total.

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

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25 Jan 2013, 02:43
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Let us first look at answer choice C and try to understand how does it strengthens the conclusion of ecologists.
Conclusion:The result says that the population of black earthworms is now almost equal to that of the red-brown earthworm, solely stemming from the blackening of the woods.
C says that "Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm".
Since climate favours the survival of red-brown worm than to the black worm, then chances are quite high that the # of red-brown worms must be very high if compared to that of black worm. Even then, the # of black worms is equal to # of red-brown worms, then something must have been wrong and some factor has played a role. What C does is that it eliminates any other chance and brings to us that the only way # of red-brown worms is equal to # of black worms is due to the blackening of woods.

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

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05 Jun 2013, 03:07
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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, 03:11, 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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27 Oct 2013, 21:04
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TGC 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.

source:Veritas prep

What is wrong with option
[Reveal] Spoiler:
(A).
As we have to prove that after factory operations the red ones were more visible than the black ones ,so this should provide support to "Black = Red solely stemming from the" blackening of the woods."
Knowing that factory operations was the cause of " blackening of the woods."

A great answer from pqhai to a great question. I would only add my few points in it.

IMO, this question though worded as strengthen question is actually testing whether we can figure out the defender assumptions the author has made while drawing the conclusion.

In general there are two types of assumptions.

1) Supporter Assumption :- This types of assumptions are common and plays traditional linking role - connecting the pieces of the arguments to one another by usually providing new information and filling out the gap between premises and conclusion.

2) Defender Assumptions :- These are of altogether different type. They protect the argument by eliminating the ideas that could weaken the argument.

Consider the following argument :- People who read a lot are more intelligent than other people. Thus, reading must cause a person to be intelligent.

Following are some of the statements that could attack the above conclusion
1) Regular exercise causes a person to be intelligent.
2) A high-protein diet causes a person to be intelligent.

So to hold the conclusion true, author assumes that the above scenarios do not exist.
1) Regular exercise does not cause a person to be intelligent
2) A high-protein diet does not cause a person to be intelligent.

So we can infer that defender assumptions are basically eliminates the possibility of any alternate explanation for the given effect.

Back to the question...........

Premise 1 :- During 1980s population of red-worms was approx 5 times that of black worms, because the coloring of red-worms was matching with the surrounding environment (esp tree's woods) and protecting them from predators.

Premise 2 :- During 1990s emissions from newly built factory blackened much of the woods. This change took back the color match advantage that red-worms were getting till date.

Premise 3 :- At the same time population of red worms became almost equal to that of black worms.

Conclusion :- The decrease in the population of red-worms is due to the blackening of the woods.

Here the ecologist attributed the decrease of red-worms' population solely to the blackening of the woods caused by emission. So while drawing this conclusion he must have assumed that any alternate explanation for the decrease in population of red-worms does not exists.

Since we are told to strengthen the ecologist's conclusion, our job is to refute the possibility of any alternate explanation.

Choice A :- INCORRECT. Shell Game Answer. This choice merely restates the premise. It does not add any new information that would affect the conclusion.

Choice B :- INCORRECT. This choice does not make any sense with the conclusion. If the predators had preferred black worms over red-worms then the population of red-worms certainly would have not dropped substantially.

Choice C :- CORRECT. Changed environmental condition could also be the cause of decrease in red-worms' population. THIS CHOICE eliminates the possibility of existence of such scenario and makes the ecologist's conclusion valid.

Choice D :- INCORRECT. irrelevant

Choice E :- INCORRECT. irrelevant.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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21 Apr 2013, 23:26
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umeshpatil wrote:
pqhai, +2 kudos for you . Very Nice explanation for this difficult question.

Do you have any generic suggestion to deal with CAUSES & EFFECTS and COMPARISON

Dear umeshpatil:
Thank you so much. I really appreciate!!! .

I guess you have practiced a lot for CR. However, from my own experience, there are two very popular types of cause and effect OR C&F with comparison in GMAT.

TYPE 1: Cause and Effect between A & B.
Logic of GMAC is:
If A and B both occur.
Conclusion: A causes B happen.
Assumption is: B does not cause A happen.

For example: People who have high GMAT score test always wear nearsighted glasses.
Conclusion: wearing nearsighted glasses makes people get high GMAT score.
Assumption: Having high GMAT score does not make people have eyes problem, leading to wearing nearsighted glasses.

TYPE 2: Mix of Cause & Effect AND comparison.
Logic of GMAC is:
Before Event X: A was LESS than B.
After Event X: A equals B. OR A is larger than B.
Conclusion: X must cause A increase.
Assumption is: No factors make B decrease

For example: Like the question we discuss in this thread.

You will see the two question types above present in CR over and over again. When you see two things both happen, and then conclude A causes B. Or when you see before event A, after event X ==> think about cause and effect. You can pick the correct answer in your mind, even when you haven't seen the answers.

I Hope it helps you a little bit.

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

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19 Jan 2013, 23:55
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Actually, IMO, A weakens the argument.
A says that the number of red worms decreased steadily. So it brings up another factor behind the equalling of the number of black and red worms. Chances can be quite high that because of the factory operations, the # of red worms decreased. So where is the factor of "blackening of wood"? Hence it weakens.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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20 Jan 2013, 00:11
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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.

Premise states that due to
"Red Color" of wood red -worms were not easily preyed upon,while the blacks were so R = 5 times the B

As stated in RED quoted above .

Industry set -up => Blackening of woods => easy contrast for REDS bad contrast for BLACKS => Drop in numbers of RED which supports the conclusion in green ,this causal relation as I mentioned above supports the conclusion . Doesn't it?
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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19 Apr 2013, 17:46
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Marcab wrote:
Since climate favours the survival of red-brown worm than to the black worm, then chances are quite high that the # of red-brown worms must be very high if compared to that of black worm. Even then, the # of black worms is equal to # of red-brown worms, then something must have been wrong and some factor has played a role. What C does is that it eliminates any other chance and brings to us that the only way # of red-brown worms is equal to # of black worms is due to the blackening of woods.

Regards.

I can say the same thing with B: "The birds that prey on earthworms prefer black worms to red-brown worms." B also suggests, just like C, that despite birds' preference to black worms, they are now equal in number to red brown worms. This can strengthen the conclusion well.

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

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20 Apr 2013, 11:45
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BangOn wrote:
I understand why C is better but can you help me explain why D is bad?
Another POV can be that since life spans have not changed, so blackening is doing the damage. This is like other things remaining same, blackening is an issue.

VERY GOOD question!
Sorry for not explaining D. Here is it.

D only says the AVERAGE life span of earthworms unchanged. Let analyze an example.

Before: The number of Red earthworms is five times that of Black earthworms. (100 vs 20)

There are 20 Black earthworms (BW), their life span is 11 days
There are 100 Red earthworms (RW), their life span is 5 days
Average life span = [20*11 + 100*5] / 120 = 6 days

After. The number of Red earthworms equals that of Black earthworms. (20 vs 20)

There are 20 BW, their life span is 11 days
There are 20 RW, their life span is 1 day (Let say, Emission from factory affected only RW, leading to RW reduced both its number and its life span. Blackening did not affect BW at all)
Average life span = [20*11 + 20*1] /40 = 6 days

Now you understand why AVERAGE life span does not help anything?

Hope it helps you.

Regards.
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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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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.

Last edited by broall on 26 May 2017, 19:58, 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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15 May 2014, 14:06
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TGC 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.

kinjiGC wrote:
Hi Mike,
Can you please explain why Option B) is wrong here :
Thanks,
Kinjal

Dear Kinjal,
I'm happy to respond. I will note that Marcab, pqhai, and Narenn have all made excellent comments on this question.

Conclusion: "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."
That highlighted word, "solely," is a hugely important word in this conclusion. We are trying to claim that the two type of earthworms now have close to equal population because of the blackening of the woods AND because of absolutely nothing else. That's the conclusion we are trying to support.

Let's look at (B):
(B) The birds that prey on earthworms prefer black worms to red-brown worms.
First of all, if the birds are eating the black worms, they must be seeing them, which means that the blackening isn't really doing much to protect them. Moreover, we have here one predator, the birds, applying selective pressure on the black earthworms, pushing there population down. In order for the two types of earthworms to be more-or-less equal in population, either something else must be accounting for more black earthworms, or something else must be accounting for fewer red-brown earthworms. Something else. Is it the blackening of the woods? Other predators? Environmental conditions? Maybe. We don't know. This is, at best, a pretty lame strengthener, because the most we can conclude is that something is hurting the red-brown earthworms or helping the black earthworms, but we don't know what.

Does all this make sense?
Mike
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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02 Jun 2014, 01:48
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Expert's post
TGC 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.

source:Veritas prep

What is wrong with option
[Reveal] Spoiler:
(A).
As we have to prove that after factory operations the red ones were more visible than the black ones ,so this should provide support to "Black = Red solely stemming from the" blackening of the woods."
Knowing that factory operations was the cause of " blackening of the woods."

As requested, here are my thoughts on the question:

Premises:
Two types of worms - red and black
Red has better camouflage from predatory birds and hence its population was 5 times that of black
Factory has blackened woods and now population of both is same (implying that black has better camouflage than before now due to blackening of woods)

Conclusion:
Blackening of woods (and hence better camouflage from predatory birds) is solely responsible for equalization of the two populations.

We need to strengthen the conclusion. Note that there is no doubt that blackening of the woods is responsible for equalization of populations. The question is whether it is solely responsible.

Option (C) tells you that another factor that could have had an effect (i.e. climate) is not responsible. This strengthens the conclusion that better camouflage is SOLELY responsible. It doesn't prove the conclusion beyond doubt since there could still be another factor that could be responsible but it does discard one of the other factors. So it does improve the probability of the conclusion being true.

Note that option (B) strengthens that 'blackening of the woods is responsible for equalization of population' but it DOES NOT strengthen that 'blackening of the woods is SOLELY responsible for equalization'. - That is where the difference lies between (B) and (C)
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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20 Apr 2013, 02:24
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pqhai wrote:
Tough question. This is an example of the combination of CAUSES & EFFECTS and COMPARISON.

MAIN IDEA:

Before event A, X is less than Y.
After event A, X and Y are equal
Conclusion: Event A causes X increase.

Assumption: Y does not decrease itself or there's NO factors make Y decrease.

Negation to confirm: If Y decreases itself ==> cannot say Event A causes X increase (because X is the same, only Y decreases to make two variables are equal).

(A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
Wrong. Actually A weakens the conclusionn not strengthen because it says red-brown earthworms decreased by itself.

(B) The birds that prey on earthworms prefer black worms to red-brown worms.
Wrong.. Shell game. Birds prefer black worms ==> why birds prefer black worms, because birds can see black worms ==> if they cannot see black worms, how can they prefer them? ==> we can infer that the blackening of the woods does not play any role to help black worms.

(C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
Correct. C definitely says the number of red worms does not decrease, even red worms increased their population more than in 1980 ==> However, the number of black worms equals to that of red worms ==> the the blackening of the woods must play an important role to help black worms.

(D) The average life span of the earthworms has remained the same since the factory began operations.
Wrong.. D does not help anything to clarify why the number of black worms increased.

(E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Wrong.. Apposite answer. Factory reduces emission ==> woods are less blacken ==> But the number of earthworm increase ==> the blackening of the woods does not play any role.

Hope it helps.

I understand why C is better but can you help me explain why D is bad?
Another POV can be that since life spans have not changed, so blackening is doing the damage. This is like other things remaining same, blackening is an issue.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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20 Apr 2013, 02:25
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pqhai wrote:
Tough question. This is an example of the combination of CAUSES & EFFECTS and COMPARISON.

MAIN IDEA:

Before event A, X is less than Y.
After event A, X and Y are equal
Conclusion: Event A causes X increase.

Assumption: Y does not decrease itself or there's NO factors make Y decrease.

Negation to confirm: If Y decreases itself ==> cannot say Event A causes X increase (because X is the same, only Y decreases to make two variables are equal).

(A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
Wrong. Actually A weakens the conclusionn not strengthen because it says red-brown earthworms decreased by itself.

(B) The birds that prey on earthworms prefer black worms to red-brown worms.
Wrong.. Shell game. Birds prefer black worms ==> why birds prefer black worms, because birds can see black worms ==> if they cannot see black worms, how can they prefer them? ==> we can infer that the blackening of the woods does not play any role to help black worms.

(C) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
Correct. C definitely says the number of red worms does not decrease, even red worms increased their population more than in 1980 ==> However, the number of black worms equals to that of red worms ==> the the blackening of the woods must play an important role to help black worms.

(D) The average life span of the earthworms has remained the same since the factory began operations.
Wrong.. D does not help anything to clarify why the number of black worms increased.

(E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Wrong.. Apposite answer. Factory reduces emission ==> woods are less blacken ==> But the number of earthworm increase ==> the blackening of the woods does not play any role.

Hope it helps.

I understand why C is better but can you help me explain why D is bad?
Another POV can be that since life spans have not changed, so blackening is doing the damage. This is like other things remaining same, blackening is an issue.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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21 Apr 2013, 16:27
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pqhai, +2 kudos for you . Very Nice explanation for this difficult question.

Do you have any generic suggestion to deal with CAUSES & EFFECTS and COMPARISON

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

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05 Jun 2013, 03:31
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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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24 Aug 2013, 10:32
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pjaseem wrote:

In the Type 2 , According to you the Assumption is : No other factors caused the reduction in B.

But in Answer C we are just talking about how the climate had no caused the reduction.It may be that water was scarce and the Red ones needed more moisture compared to the blanck ones , hence they died enmasse.How can C strenghten the argument then?

Hi pjaseem

C says the climate is favorable for RED worm population. So the RED worm population should increase or at least as much as in the past (the RED worm population did NOT decrease as you said).
For example:
In the past: RED worm population was 100, Black worm population was 20 (1/5 of 100)
After new manufacturing: RED worm population was 150, black worm population was 150 too.
==> Clearly the new factor "the blackening of the woods" should play important role to support the Black worm population. Hence, C strengthens the conclusion.

Note: Strengthen does not mean support 100%. Even the answer supports 1%, it DOES strengthen the conclusion.

Hope it helps.
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink]

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25 Jan 2013, 02:13
hey...even i think that the answer should be A....Can someone explain Y the ans is C?

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

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25 Jan 2013, 03:17
great explanation...thanx alot...

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Re: Two types of earthworm, one black and one red-brown, inhabit   [#permalink] 25 Jan 2013, 03:17

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