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To prevent a newly built dam on the Chiff River

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To prevent a newly built dam on the Chiff River [#permalink]

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To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 03 Sep 2015, 06:05
I am not sure about the Original Answer choice, We don't know how the toxic water affects the fish. It is not clearly mentioned in the answer choice that toxic water kills the fish.

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 03 Sep 2015, 06:06
I am not sure about the Original Answer choice, We don't know how the toxic water affects the fish. It is not clearly mentioned in the answer choice that toxic water kills the fish.
Any help would be appreciated.
Thanks and Regards.

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To prevent a newly built dam on the Chiff River [#permalink]

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Hi drashi,
A weakener just needs to create a doubt in the conclusion. Toxic water may not have killed the fish. But there's a possibility that it could have. In that case, the option weakens the given conclusion.

The author's conclusion is that the fish pass is defective. The basis for this conclusion is that in the first season after the project's completion, only 300 per day made the journey whereas before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season.

Possible weakeners for the conclusion:

300 per day doesn't necessarily mean that the fish pass is defective. It could mean:

1) The fish population has gone down.
2) Fish have found a different place other than upstream to go to.

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
-> This is outside the scope of the conclusion. We arent interested in fish that have already migrated upstream.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
-> We arent interested in what's happening on other rivers in the region.

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
-> This is a possible weakener. Toxic river sediments may have brought down the fish population. This is also in accordance with our prethinking.

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
-> This is rather a strengthener. Slight decrease in pouplation doesnt help us to rule out the decrease in population aspect. According to this statement there was no reason why the fish didnt go upstream. Fish pass could thus have been the reason.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
-> This again rules out the possibility that sufficient water wasnt available to go upstream. This is a strenghthner.

Hence, C is the answer.

Hope this helps.

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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dgr8sandeep wrote:
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.



Got it correct "C" Coz if the dam poured in toxic into downstream fish may have died so less fish made the journey not because of defective fish pass.

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 20 Aug 2016, 07:37
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.


Before fish pass = 1000 fish passes through the dam
After fish pass = 300 fish passes through the dam
the fish pass is defective. Assumption here is :-

1> same fish population before and after the dam building.
2> Some other place fish have found

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
If fish have migrated and don't return back, although fish population in cliff river has decreased but assumption here is now river has only 300 fish. so this time its only 300 fish that are migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream. : It doesn't mean that this fish pass can not be defective.


(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.


(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream:- strengthen the argument by saying that migratory fish is getting more helped by flow of dam water.

Confused bet A,C,D

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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abrakadabra21 wrote:
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.


Before fish pass = 1000 fish passes through the dam
After fish pass = 300 fish passes through the dam
the fish pass is defective. Assumption here is :-

1> same fish population before and after the dam building.
2> Some other place fish have found

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
If fish have migrated and don't return back, although fish population in cliff river has decreased but assumption here is now river has only 300 fish. so this time its only 300 fish that are migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream. : It doesn't mean that this fish pass can not be defective.


(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.


(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream:- strengthen the argument by saying that migratory fish is getting more helped by flow of dam water.

Confused bet A,C,D


Conclusion : The fish pass is defective. (X)

Premise : Fishes migrating through the pass has reduced. (Y)

We have X causes Y.

Lets break it. :-D

Option (A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again. : Is this a change after the pass or was it happening before also? If before, then it implies it has nothing to do with the conclusion and if after, it implies conclusion is strengthened. Hence , Incorrect.

Option (C) : The construction of the dam stirred up potentially toxic river sediments that were carried downstream. -- Alternate cause for the decrease in number. Hence, weakens the conclusion.

Option (D) : Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years. -- Irrelevant. If it is happening then why did the journey actually reduced after the construction itself. It should have followed the same trend.

Note : We need to find something that explains what happens after construction that made the journey reduction.

Hence, C is the best option with an alternate cause.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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Not a very convincing question & answer, I'd say. We are not supposed to bring in our understanding of how the world works, when we solve these questions. How do we know that potentially toxic sediments are harmful for the fish?
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To prevent a newly built dam on the Chiff River [#permalink]

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New post 02 May 2017, 16:52
dgr8sandeep wrote:
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.


GMATNinja DmitryFarber GMATNinjaTwo

What is the better approach to solve this question?

A fish pass was designed to allow fish to migrate upstream past the dam to their breeding grounds. The number of migrating fish fell from 1000++/day before the dam was built to 300/day in the first season after it was built, indicating - according to the argument - that the fish pass is defective.

We made this fish dam, The next year, very few fish appeared. So there must be something wrong with the fish pass. To weaken that, we want to say, no. There is SOME OTHER REASON there are very few fish this year.

Why (E) will NOT actually weaken the argument? It still allow fish to migrate upstream.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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dgr8sandeep wrote:
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.


Responding to a pm:

Premises:
A fish pass is made on the new dam to allow fish to swim upriver to spawn.
Before the dam, several 1000 fish swam upriver every day.
Now only 300 do per day.

Conclusion: Fish pass is defective.

We have to weaken the argument. So we have to think about why fewer fish may be swimming upstream though the fish pass may not be defective.

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
Irrelevant. What happens to them after the migrate, we don't care. We want to know why they are not migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
This strengthens that our fish pass is defective! At other places, the decrease is less. We are seeing a huge decrease.

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
This provides us a reason why fewer fish are swimming upriver. Perhaps because there are fewer fish now. The construction introduced toxic substances in the river which should have killed many fish. Hence, the fish pass may not be faulty. The problem may be that we have fewer fish now.
Correct.

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
The population has been declining slightly over many years. It doesn't explain the huge decrease in the number of fish swimming upriver.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
The dam is aiding the fish by providing enough water for them to swim upstream. So the fewer fish swimming upstream would not be expected. Hence defective fish pass could actually be the reason.

Answer (C)
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 03 May 2017, 01:08
Is it correct to assume that the number of fish is reduced/fish died due to potentially toxic sediments? Nothing is mentioned in this argument about this.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 03 May 2017, 04:32
Mahmud6 wrote:
Is it correct to assume that the number of fish is reduced/fish died due to potentially toxic sediments? Nothing is mentioned in this argument about this.


Yes, it is not mentioned specifically but it alludes to a reason other than a faulty fish pass. That weakens our conclusion. Note that we don't have to establish that the conclusion cannot hold. We just have to make one doubt it, just weaken it.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 03 May 2017, 04:38
ziyuen wrote:

GMATNinja DmitryFarber GMATNinjaTwo

What is the better approach to solve this question?

A fish pass was designed to allow fish to migrate upstream past the dam to their breeding grounds. The number of migrating fish fell from 1000++/day before the dam was built to 300/day in the first season after it was built, indicating - according to the argument - that the fish pass is defective.

We made this fish dam, The next year, very few fish appeared. So there must be something wrong with the fish pass. To weaken that, we want to say, no. There is SOME OTHER REASON there are very few fish this year.

Why (E) will NOT actually weaken the argument? It still allow fish to migrate upstream.


Can I try to help you please? :)

I think you didn't understand the argument clearly.

It is saying during the spawning season fishes migrate to upstream. " swam upriver during spawning season".

Option E is saying Dam is actually helping fishes by making them move upstream, which is the goal of fishes. So, ideally there should be an increase in the number of fishes after the dam. But this never happened. So, E is not providing us any alternative cause of why there was a decrease. So, E is not the correct answer.

In option C, we have an alternate cause that shows the decrease in the number was due to some toxic material. Hence, C is the correct answer.

Mahmud6 wrote:
Is it correct to assume that the number of fish is reduced/fish died due to potentially toxic sediments? Nothing is mentioned in this argument about this.


Yes, it is actually. So, this point is making us weaken our conclusion that may be Dam is not defective but these toxins are killing the fishes. Hence, an alternate reason for the decrease and a weakener to our conclusion. After reading option C, I can doubt the validity of the argument, our goal as per the question.

Let me know in case of any confusion. :)
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 27 May 2017, 09:17
Hi Karishma,

I did get the question right but somehow I'm not being able to reject A on solid ground. What if the fish are migrating up and not coming back. In that case there will be lesser fish to migrate up anyway, right? I can't seem to wrap my head around why not A.

Please help.

Best,
Snigdha

VeritasPrepKarishma wrote:
dgr8sandeep wrote:
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.


Responding to a pm:

Premises:
A fish pass is made on the new dam to allow fish to swim upriver to spawn.
Before the dam, several 1000 fish swam upriver every day.
Now only 300 do per day.

Conclusion: Fish pass is defective.

We have to weaken the argument. So we have to think about why fewer fish may be swimming upstream though the fish pass may not be defective.

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
Irrelevant. What happens to them after the migrate, we don't care. We want to know why they are not migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
This strengthens that our fish pass is defective! At other places, the decrease is less. We are seeing a huge decrease.

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
This provides us a reason why fewer fish are swimming upriver. Perhaps because there are fewer fish now. The construction introduced toxic substances in the river which should have killed many fish. Hence, the fish pass may not be faulty. The problem may be that we have fewer fish now.
Correct.

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
The population has been declining slightly over many years. It doesn't explain the huge decrease in the number of fish swimming upriver.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
The dam is aiding the fish by providing enough water for them to swim upstream. So the fewer fish swimming upstream would not be expected. Hence defective fish pass could actually be the reason.

Answer (C)

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 27 May 2017, 09:26
ss18 wrote:
Hi Karishma,

I did get the question right but somehow I'm not being able to reject A on solid ground. What if the fish are migrating up and not coming back. In that case there will be lesser fish to migrate up anyway, right? I can't seem to wrap my head around why not A.

Please help.

Best,
Snigdha


Hi ss18 ,

Let me help you here.

Our conclusion is Dam is defective. This conclusion is drawn on the basis of the premise "Upriver movement has reduced".

Now A is saying they are not returning back. How does that tell us the movement has reduced? We are only concerned about those fishes that are moving from downstream to upstream. So, whether they are coming back is OFS.

I know why you are confused. You are assuming that those going upstream will return and then again would like to go back. But my friend, this is your assumption which is not valid here.

What we are bothered about is the movement from downstream to upstream. May be fishes move only from downstream to upstream during that spawning season but this time the number of such fishes has reduced.

Hence, A is OUT.

C is clearly providing us the reason that fishes are getting killed and thus not able to move upstream.

I hope that makes sense. Reach out in case of any concern.
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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 27 May 2017, 09:35
Thank you. It does make sense. I did choose C but just wasn't able to say a strong no to A. I do realise that in order for A to work, multiple assumptions have to be made. In fact you pointed that out as well.

A huge thank you for such a prompt reply! I truly appreciate it.

Best,
SS18

abhimahna wrote:
ss18 wrote:
Hi Karishma,

I did get the question right but somehow I'm not being able to reject A on solid ground. What if the fish are migrating up and not coming back. In that case there will be lesser fish to migrate up anyway, right? I can't seem to wrap my head around why not A.

Please help.

Best,
Snigdha


Hi ss18 ,

Let me help you here.

Our conclusion is Dam is defective. This conclusion is drawn on the basis of the premise "Upriver movement has reduced".

Now A is saying they are not returning back. How does that tell us the movement has reduced? We are only concerned about those fishes that are moving from downstream to upstream. So, whether they are coming back is OFS.

I know why you are confused. You are assuming that those going upstream will return and then again would like to go back. But my friend, this is your assumption which is not valid here.

What we are bothered about is the movement from downstream to upstream. May be fishes move only from downstream to upstream during that spawning season but this time the number of such fishes has reduced.

Hence, A is OUT.

C is clearly providing us the reason that fishes are getting killed and thus not able to move upstream.

I hope that makes sense. Reach out in case of any concern.



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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 23 Aug 2017, 11:11
C is the correct choice - the statement suggests that the toxic sediments may have poisoned the fish and reduced their population. A smaller fish population could be sufficient to explain the reduced number of fish migrating, which casts doubt on the argument's assumption that the explanation for their declining numbers involves the fish pass.
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To prevent a newly built dam on the Chiff River [#permalink]

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New post 26 Aug 2017, 06:42
Hi mikemcgarry

I am afraid I need you help

To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream
.

I picked up E, because,
in the prompt, it states thousands fish swam a per day during spawning season, but in the first season only 300 per day swam, the decreased number is between different seasons.
While choice E states that dam release sufficient water in spawning season, hmmm, E points out a reason, sufficient water from dam, that thousands fish swam, I can get the reason that no sufficient water in the first season after building dam, leading few fish swam,
in other words, it eliminates the factor -- fish pass defective,

Please point out my fault.

Thanks in advance

Have a nice day

>_~

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 01 Sep 2017, 01:12
construction of bridge let that happen but there is no defect in the pass

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Re: To prevent a newly built dam on the Chiff River [#permalink]

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New post 10 Sep 2017, 14:19
VeritasPrepKarishma wrote:
dgr8sandeep wrote:
(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
Irrelevant. What happens to them after the migrate, we don't care. We want to know why they are not migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
This strengthens that our fish pass is defective! At other places, the decrease is less. We are seeing a huge decrease.

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
This provides us a reason why fewer fish are swimming upriver. Perhaps because there are fewer fish now. The construction introduced toxic substances in the river which should have killed many fish. Hence, the fish pass may not be faulty. The problem may be that we have fewer fish now.
Correct.

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
The population has been declining slightly over many years. It doesn't explain the huge decrease in the number of fish swimming upriver.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
The dam is aiding the fish by providing enough water for them to swim upstream. So the fewer fish swimming upstream would not be expected. Hence defective fish pass could actually be the reason.

Answer (C)


Thank you for your illustrations. I chose A because, when it says these fish are not returning, this offers an explanation that the population of the downstream only decreases, thus making a possibility why only 300 fish made it through the gate(300 fish may be a good level after this population decrease). Is there anything not appropriate with this logic?

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Re: To prevent a newly built dam on the Chiff River   [#permalink] 10 Sep 2017, 14:19

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