Find all School-related info fast with the new School-Specific MBA Forum

It is currently 22 Oct 2014, 06:38

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

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

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
4 KUDOS received
Director
Director
avatar
Joined: 03 Aug 2012
Posts: 914
Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
Followers: 13

Kudos [?]: 239 [4] , given: 318

Premium Member CAT Tests
Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 19 Jan 2013, 22:16
4
This post received
KUDOS
10
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

25% (02:39) correct 75% (01:35) wrong based on 930 sessions
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."
[Reveal] Spoiler: OA

_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Veritas Prep GMAT Discount CodesKnewton GMAT Discount CodesKaplan GMAT Prep Discount Codes
Expert Post
3 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Status: Preparing for the another shot...!
Joined: 03 Feb 2011
Posts: 1425
Location: India
Concentration: Finance, Marketing
GPA: 3.75
Followers: 129

Kudos [?]: 644 [3] , given: 62

GMAT ToolKit User Premium Member
Re: Two types of earthworm, one black and one red-brown [#permalink] New post 19 Jan 2013, 22:55
3
This post received
KUDOS
Expert's post
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.
_________________

Prepositional Phrases Clarified|Elimination of BEING| Absolute Phrases Clarified
Rules For Posting
www.Univ-Scholarships.com

Director
Director
avatar
Joined: 03 Aug 2012
Posts: 914
Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
Followers: 13

Kudos [?]: 239 [0], given: 318

Premium Member CAT Tests
Re: Two types of earthworm, one black and one red-brown [#permalink] New post 19 Jan 2013, 23:11
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?
_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Intern
Intern
avatar
Joined: 23 Jan 2013
Posts: 6
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: Two types of earthworm, one black and one red-brown [#permalink] New post 25 Jan 2013, 01:13
hey...even i think that the answer should be A....Can someone explain Y the ans is C?
Expert Post
15 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Status: Preparing for the another shot...!
Joined: 03 Feb 2011
Posts: 1425
Location: India
Concentration: Finance, Marketing
GPA: 3.75
Followers: 129

Kudos [?]: 644 [15] , given: 62

GMAT ToolKit User Premium Member
Re: Two types of earthworm, one black and one red-brown [#permalink] New post 25 Jan 2013, 01:43
15
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
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.
_________________

Prepositional Phrases Clarified|Elimination of BEING| Absolute Phrases Clarified
Rules For Posting
www.Univ-Scholarships.com

Intern
Intern
avatar
Joined: 23 Jan 2013
Posts: 6
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: Two types of earthworm, one black and one red-brown [#permalink] New post 25 Jan 2013, 02:17
great explanation...thanx alot...
1 KUDOS received
Intern
Intern
avatar
Joined: 23 Jan 2011
Posts: 12
Followers: 0

Kudos [?]: 1 [1] , given: 9

GMAT ToolKit User
Re: Two types of earthworm, one black and one red-brown [#permalink] New post 19 Apr 2013, 16:46
1
This post received
KUDOS
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.
24 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [24] , given: 122

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 19 Apr 2013, 22:43
24
This post received
KUDOS
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.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.


Last edited by pqhai on 20 Apr 2013, 10:57, edited 4 times in total.
Manager
Manager
avatar
Joined: 27 Feb 2012
Posts: 138
Followers: 1

Kudos [?]: 20 [0], given: 22

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 20 Apr 2013, 01:24
1
This post was
BOOKMARKED
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 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.
_________________

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Please +1 KUDO if my post helps. Thank you.

Manager
Manager
avatar
Joined: 27 Feb 2012
Posts: 138
Followers: 1

Kudos [?]: 20 [0], given: 22

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 20 Apr 2013, 01:25
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 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.
_________________

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Please +1 KUDO if my post helps. Thank you.

2 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [2] , given: 122

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 20 Apr 2013, 10:45
2
This post received
KUDOS
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.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.

1 KUDOS received
Manager
Manager
User avatar
Joined: 31 May 2012
Posts: 166
Followers: 4

Kudos [?]: 68 [1] , given: 69

CAT Tests
Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 21 Apr 2013, 15:27
1
This post received
KUDOS
pqhai, +2 kudos for you :lol: . Very Nice explanation for this difficult question.

Do you have any generic suggestion to deal with CAUSES & EFFECTS and COMPARISON
3 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [3] , given: 122

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 21 Apr 2013, 22:26
3
This post received
KUDOS
umeshpatil wrote:
pqhai, +2 kudos for you :lol: . 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.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.

Manager
Manager
avatar
Joined: 21 Aug 2012
Posts: 150
Followers: 2

Kudos [?]: 36 [0], given: 41

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

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.


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
_________________

MODULUS Concept ---> inequalities-158054.html#p1257636
HEXAGON Theory ---> hexagon-theory-tips-to-solve-any-heaxgon-question-158189.html#p1258308

Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [0], given: 122

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

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.


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

Your logic is not correct.
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.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.

Intern
Intern
avatar
Joined: 16 Mar 2013
Posts: 24
Location: United States
Concentration: International Business, Entrepreneurship
Schools: NTU '15 (S)
GPA: 3.08
WE: Marketing (Manufacturing)
Followers: 0

Kudos [?]: 9 [0], given: 6

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 24 Aug 2013, 02:34
pqhai wrote:
umeshpatil wrote:
pqhai, +2 kudos for you :lol: . 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?
Intern
Intern
avatar
Joined: 16 Mar 2013
Posts: 24
Location: United States
Concentration: International Business, Entrepreneurship
Schools: NTU '15 (S)
GPA: 3.08
WE: Marketing (Manufacturing)
Followers: 0

Kudos [?]: 9 [0], given: 6

Re: Two types of earthworm, one black and one red-brown [#permalink] New post 24 Aug 2013, 02:37
Marcab wrote:
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.



Your reasoning is flawed.C just eliminates one cause "climatic conditions" . We still have to make the assumption (if C is right) that there are no other causes for the phenonmenon
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [0], given: 122

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 24 Aug 2013, 09:32
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.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.

Intern
Intern
avatar
Joined: 30 Oct 2011
Posts: 43
Followers: 0

Kudos [?]: 4 [0], given: 12

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 27 Aug 2013, 02:32
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.


Hi pqhai, not sure why but I am still not able to get why 'B' is not as good an option as 'C'. Please help me understand where I am wrong.

My reasoning - The birds that prey on earthworms prefer black worms to red-brown worms: Now, because of the blackening of the wood; the birds can not see the black ones i.e. the black worms camouflage the black wood and can not be prey by the birds, hence are almost equal in no. to the red brown worms.

Though the reasoning is the same as explained by you for 'C', I still don't see why 'C' is a better option than 'B'.

Thank you in advance!
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 15 Jun 2012
Posts: 1120
Location: United States
Followers: 136

Kudos [?]: 1374 [0], given: 122

Re: Two types of earthworm, one black and one red-brown, inhabit [#permalink] New post 27 Aug 2013, 13:20
mneeti wrote:

Hi pqhai, not sure why but I am still not able to get why 'B' is not as good an option as 'C'. Please help me understand where I am wrong.

My reasoning - The birds that prey on earthworms prefer black worms to red-brown worms: Now, because of the blackening of the wood; the birds can not see the black ones i.e. the black worms camouflage the black wood and can not be prey by the birds, hence are almost equal in no. to the red brown worms.

Though the reasoning is the same as explained by you for 'C', I still don't see why 'C' is a better option than 'B'.

Thank you in advance!


Hi mneeti.

I'm glad to help.

There are two notes for your inquiry:

(1) The question stem asks you find the answer that MOST strengthen the conclusion
It means even when you see two options that can strengthen a conclusion, but one option is better ==> The other one is incorrect answer because it does not strengthen the conclusion the most.

(2) I don't think your logic for B is wrong, but it has weakness.
Your reasoning is: the bird prefers black worms to red-brown worms, however, the bird does not see the black earthworms (because of the blackening effect) ==> the black wood and can not be prey by the birds. ==> its population increase. ==> B strengthens the conclusion.

Let see an example: you prefer green apples to red apples. There are two apple - one green and one red- putting on a green table. You are asked: "which apple you like?" There would be two scenario:
- You can see the green apple. Clearly, you say "I like the green one". ==> The green table does not help to camouflage the green apple.
- You can NOT see the green apple. Clearly, you have only one option, the red apple. How can you pick the green apple that you prefer if you can't see it? ==> This scenario is illogical.

Back to the option B:
The work "Prefer" is key. Logically, you "prefer" A to B only if you're able to distinguish A and B. If you're not able to do so, A or B does not matter, cause they look the same. Thus, the fact that the bird "prefers" the black earthworm indirectly implies that the bird is able to distinguish the black earthworm and the red earthworm. If the bird is not able to distinguish the black one and the red one, the bird has only option - the red earthworm. The bird can NOT prefer the black earthworm. ==> the blackening effect does not help to camouflage the black earthworm. Hence, B does not help to strengthen the conclusion.

In short, the reasoning of B may or may not be correct. Thus, it has weakness for criticism and cannot strengthen the conclusion the MOST . ==> B is incorrect answer.

Hope it helps.
_________________

Please +1 KUDO if my post helps. Thank you.

"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."

Chris Bangle - Former BMV Chief of Design.

Re: Two types of earthworm, one black and one red-brown, inhabit   [#permalink] 27 Aug 2013, 13:20
    Similar topics Author Replies Last post
Similar
Topics:
Admitted to two, waitlisted to one force 0 05 Jun 2014, 07:42
10 Two types of earthworm, one black and one red-brown, inhabit srabani88 4 05 Jun 2013, 01:31
2 Experts publish their posts in the topic One equation,...two variables?? stilite 2 10 Sep 2009, 08:08
A diagram has exactly two black dots and one green dot for jallenmorris 7 15 May 2008, 14:11
One black, one red, one blue and two white pearls are oxon 9 07 Nov 2004, 14:14
Display posts from previous: Sort by

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

  Question banks Downloads My Bookmarks Reviews Important topics  

Go to page    1   2    Next  [ 29 posts ] 



GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.