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Two types of earthworm, one black and one red-brown, inhabit

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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 31 Aug 2013, 00:30
pqhai wrote:
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.



Sorry for the late reply.You are right about that.I think C wont be the answer if the question was "logically justify" in which case the answer has to provide 100% support
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Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 27 Oct 2013, 20:04
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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.

Brief about Defender Assumptions

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] New post 03 Dec 2013, 04:41
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).

CONSIDER EACH ANSWER:

(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.


Hi pqhai, thanks for the explanation. I got your point. However, I still don't understand why you mentioned that the conclusion was Event A causes X increase.

The argument says: 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.

It was not stated that X increased. The only thing we can observe is that the number of 2 species is equal. It can be: "Y decreased due to the change of color of the woods (they are blackened). Since the woods are no longer favorable for the camouflage of Y, its number have definitely reduced. Thus, Event A causes Y decrease." In this case, A can be right, so does D, as in the example that you mentioned.

Do I have any mistakes?

Thank you for answering my question.
Re: Two types of earthworm, one black and one red-brown, inhabit   [#permalink] 03 Dec 2013, 04:41
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