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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, 22:16
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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 Jan 2013, 22:55
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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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19 Jan 2013, 23:11
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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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25 Jan 2013, 01:13
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, 01:43
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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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25 Jan 2013, 02:17
great explanation...thanx alot...

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

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19 Apr 2013, 16:46
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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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19 Apr 2013, 22:43
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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, 10:57, 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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20 Apr 2013, 01:24
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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, 01:25
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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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20 Apr 2013, 10:45
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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.

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

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21 Apr 2013, 15:27
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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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21 Apr 2013, 22:26
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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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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.

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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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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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23 Aug 2013, 22:14
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 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.

Very nice explanations pghai..!!!

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

For option B, what i thought was that if birds prey on black worms, then the population of Black worms will reduce inspite of efforts made by factories. So this does not strengthen..

IS this correct?

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

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23 Aug 2013, 22:49
jaituteja wrote:
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 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.

Very nice explanations pghai..!!!

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

For option B, what i thought was that if birds prey on black worms, then the population of Black worms will reduce inspite of efforts made by factories. So this does not strengthen..

IS this correct?

Thanks,
Jai

Hi Jai

The conclusion is: the blackening of the woods helps the black-worm population increased.

Your logic is: birds prey black-worm ==> black-worm population decreased ==> B does not strengthen. But the fact clearly says: The populations of black worm INCREASED, not decreased.

==> Let use two first parts of your logic + Fact in the stimulus: birds prey black-worm ==> black-worm population decreased, however the population of black-worm still increased ==> Clearly the blackening of the woods HELPED the population of black-worm increase. Hence, B should strengthen. But actually, B is not correct answer. That's why I said B is SHELL GAME.

You can refer back to my explanation above for B.

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

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24 Aug 2013, 02:34
pqhai wrote:
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.

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?

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Re: Two types of earthworm, one black and one red-brown, inhabit   [#permalink] 24 Aug 2013, 02:34

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