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To prevent a newly built dam on the Chiff River from blocking the rout

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

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New post 23 Oct 2018, 02:52
VeritasKarishma wrote:
sriramsundaram91 wrote:
I guess my brain is demented. Can anyone help this demented brain understand why option A to be wrong?
I have read the experts reply. I am still not able to digest why A is wrong? Fish that have migrated upstream breeding grounds don't return the chiff river again.
If there were several thousand fishes and if they had already migrated(they would not want to go downstream for some reason). Only a few would have been left. These few would try to migrate using the fish pass thus attributing to the fewer fish that use the fish pass.


Every year, during spawning season, several 1000s of fish swim upriver to breeding grounds.
This happens during every spawning season. If the fish that have migrated do not come back, they do not come back every season. But still 1000s of fish swim upriver every day in every spawning season.

But in this spawning season (the first one after the dam got constructed), only 300 fish are swimming upriver. So either there is a problem with the fish pass or there are fewer fish or something else. Certainly, the new dam has had some impact this season.


I understand now; the fewer fish do not guarantee that there is no problem with the construction of the fish pass.
Simple yet,powerful Idea! Thanks.
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To prevent a newly built dam on the Chiff River from blocking the rout  [#permalink]

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New post 13 Dec 2018, 05:38
I used Pre-thinking technique, Now the issue is that the first thought I had was that there might have been a population decline because once the migration was done the fish never came back to their originating position. In such a scenario why option A is wrong?
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Re: To prevent a newly built dam on the Chiff River from blocking the rout  [#permalink]

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New post 13 Dec 2018, 05:46
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amansharma2988 wrote:
I used Pre-thinking technique, Now the issue is that the first thought I had was that there might have been a population decline because once the migration was done the fish never came back to their originating position. In such a scenario why option A is wrong?


Note the tone of the argument:

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.

During spawning season, several 1000 fish used to swim upriver as a habitual thing. It used to happen in every spawning season. So this was not causing decrease in population. The change happened only after the project's completion.
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New post 26 Dec 2018, 07:00
Thanks GMATNinja and VeritasKarishma for the wonderful explanations. It helped me rule out E to an extent.

I have made up a pictorial visualisation for this question, to understand it properly.
If possible, could you please assess the validity of the understanding as attached :)

My small query is:

There are two scenarios:

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.

Here we have FIRST SEASON and SPAWNING SEASON. Are they both same? How?
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File comment: Pictorial representation of the explanation.
OG_VR_Fish.PNG
OG_VR_Fish.PNG [ 273.32 KiB | Viewed 457 times ]

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

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New post 01 Jan 2019, 06:47
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rish2708 wrote:
Thanks GMATNinja and VeritasKarishma for the wonderful explanations. It helped me rule out E to an extent.

I have made up a pictorial visualisation for this question, to understand it properly.
If possible, could you please assess the validity of the understanding as attached :)

My small query is:

There are two scenarios:

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.

Here we have FIRST SEASON and SPAWNING SEASON. Are they both same? How?


Yes, we are talking about only one season and that is the spawning season. The first season after the dam opens means first spawning season.
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Re: To prevent a newly built dam on the Chiff River from blocking the rout  [#permalink]

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New post 31 May 2019, 15:19
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Oof. GMATNinja - thank you for your detailed explanations, as always. This question was one that I did this morning and have really thought about for a few hours on and off. I am trying to understand the way I think, and how I need to tweak it in order to solve GMAT problems within the tight time constraints that I need to.

In this case, I was happy to see that my thinking wasn't unique: I too thought option (A) was right. I think when you read this type of passage, it's very easy to try and contextualize it based on how you're familiar with the process. I can't say I know anything about fish and spawning, but for some reason, the passage reads to me like they should go upstream during the spawning season, and back down to hang out for the remaining duration of the year. Funnily enough, no where in the text does it say this is true.

Option (A) struck a chord with my preconceived notions and I was tricked into thinking it was right. Despite option (C) sounding so incredibly reasonable when I read it, I stuck with my 'gut' and did not find 4 wrong answers, but rather 3, and then went to familiarity. Dun dun dun. Bad move.

Thank you guys for posting on this question and sharing your thoughts, all of your contributions have been very helpful! I had a head bang moment when I realized the logic and hence answer. In this case - what goes up, does not have to come down =)
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Re: To prevent a newly built dam on the Chiff River from blocking the rout  [#permalink]

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New post 08 Aug 2019, 01:22
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?

Pre-thinking:
An assumption here is that nothing but the dam and the fish pass is an obstacle for fishes.
Let's imagine that the fish pass was designed to allow thousands of fishes a day but then because of some unexpected factor now it allows only 300 fishes per day. Since the confusion says that the fish pass is defective we can weaken this very conclusion by spotting the unexpected factor.
A weakener along these lines will be our answer.


(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
The passage clearly identifies rates before and after the dam was built. So it's irrelevant how may fishes would stay after reaching the breeding area. Hence incorrect

(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.
Opposite. This actually strengthen the conclusion that the fish pass is defective since many other fish passes do their work. Hence incorrect

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
This is our unexpected factor. We can see that the reduction in rate is due to the toxic sediments and not to the fish pass itself. Hence correct

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
Since we don't know the extend of this decrease we can not say for sure that the decrease in fish population led to a decrease in the rate. There might have been a decrease but that does not mean that thousands of fishes per day don't reach the breeding areas each day. Hence incorrect

(E) During spawning season, the dam releases sufficient water for migratory fish below the dam to swim upstream.
This choice does not have a clear impact on the conclusion since this might mean two things: #1 the dam and the fish pass are working well and there is probably another cause for the decrease in rate. #2 the fish pass is defective and it is the cause of the decrease in rate. Since this answer choice does not have a clear impact on the conclusion it is incorrect
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To prevent a newly built dam on the Chiff River from blocking the rout  [#permalink]

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New post 26 Sep 2019, 01:25
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 for migratory fish below the dam to swim upstream.


Conclusion: Fish pass is defective.

We need to weaken the argument. So, we need find an alternate reason why the less migration and solution shouldn't involve fish pass at all.

A: Alternate reason yes. Contender.
B: It's a strengthener. rejected
C: Alternate reason yes. Contender.
D: Irrelevant. rejected
E: It's a strengthener. rejected

Between A and C. let's review the thought

Let's say A is true but does it necessarily break the argument. What if the fish is not returning due to a defect in fish pass. Since the solution may involve a fish pass. It is inconclusive. Moreover, the argument also mentions that it is the first season after fish pass involvement. This furthers our argument that the argument is inconclusive.
C mentions a solution which does not involve a fish pass. Therefore, C.
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