Manatees, aquatic mammals inhabiting Florida’s rivers and coastal

Question

Manatees, aquatic mammals inhabiting Florida’s rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats. To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds. Unfortunately, manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows. Therefore, this approach may in fact make things worse rather than better.

Which of the following, if true, casts most doubt on the conclusion?

Which of the following, if true, casts most doubt on the conclusion?

(A) The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats.

(B) Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat traffic.

(C) Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the endangered manatee population.

(D) The sound of a boat engine generally travels much further under water than it does through the air.

(E) When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal-background noise.

I marked the OA by PoE, but I was not much clear on the argument. Can someone explain on the argument and answer choice?

KarishmaB · Accepted Answer

Premises:
- To avoid manatee-boat collisions, boat traffic in manatee-populated waters is being required to maintain very low speeds.
- Manatees are unable to hear low-pitched sounds.
- A boat’s sound lowers in pitch as the boat slows.

Conclusion:
This approach (the approach is 'reducing boat speeds') may make things worse.

If we have to cast doubt on the conclusion, we have to show that reducing boat speeds may not make things worse.
Option (A): It doesn't matter how the areas were decided. This option doesn't say that reducing boat speed will not increase collisions.
Option (B): Out of scope of our question. We need to focus on boat-manatee collisions.
Option (C): Boat traffic is increasing. But it doesn't say how reducing speed may not increase number of collisions.
Option (D): It does have something to do with speed of sound. But it says that sound of a boat travels much further under water than through air. If sounds are low pitched manatees may not be able to hear them, irrespective of how far the sounds travel and how far the manatees are from the boat. Lowering of speed of boats could make the situation worse and hence, it doesn't weaken my conclusion.
Option (E): Manatees are unable to discern sounds of boat moving at different speeds over background noise. This means, it doesn't matter at what speed the boat is moving. The manatee will not be able to discern its sound (whether high pitched or low pitched). Hence, reducing the speeds of the boats will not have a negative impact on the number of collisions. It might even have some positive effect since the slow moving boat may be able to see the manatee and change its course in time. Hence, this option weakened our conclusion.
Answer (E).

Note: To weaken the conclusion, I only need to prove that the approach may not make things worse. I don't have to show that it necessarily improves matters.

krypt · Answer

I think the answer is E.

The hypothesis is that boats traveling slow = less manatees killed. However, manatees can't hear slow boats and therefore, slow boats will make the problem WORSE. The argument is saying that boats traveling at various speeds will kill less manatees than all boats traveling slowly on the account that manatees can't hear slow boats.

To cast doubt on this, we can show that manatees can't hear various speeds. Thus, mandating slow boats will not make the problem WORSE, it should stay the same.

amp0201 · Answer

Shell game is like the answer choice most similar to correct one, though not the correct one.

The argument's conclusion is - slower boats might worsen the problem.

Answer choice E says Manatees are not able to hear noises at any levels. Hence the problem won't worsen but will stay same.

Answer choice B is about faster boats and nothing to say about slower boats.

Hence I believe to be E rather than B. Thank You.

Thanks,
Akhil M.Parekh

PTK · Answer

E. 
Seemed easy to me.

because boats drive fast they kill manatee. 
Why? there are two reasons: either manatees are sluggish or deaf. 
conclusion: author says that deafness kills M. we must introduce evidence that would make author to reconsider his her conclusion by saying "ohh... I am stupid I did not account for this"

E says that M can't discern sounds, so they die not due to deafness, but becuase they are sluggish.

mejia401 · Answer

Conclusion:  Therefore, this approach may in fact make things worse rather than better.

Reasoning:   High boat speeds kills manatees. Slow boat speeds kills more manatees because manatees cannot hear any sound. To weaken the argument, the statement must provide that slow boat speeds do not kill any more than high boat speeds. (Wrong answers are neutral or provide reasons why slow boat speeds do kill more manatees than high boat speeds.)

A. The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported
collisions between manatees and boats.  Neutral. Statement does not cast doubt.

B. Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat
traffic. Wrong. Statement provides a reason why more manatees are present in waters with slow boat speeds.

C. Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the
endangered manatee population.  Neutral. More boats kill more manatees; nothing about boat speeds.

D. The sound of a boat engine generally travels much further under water than it does through the air.  Opposite answer - admittedly, this one threw me off. I forgot if this question were a strengthen or weaken, and key words such as "engine" + "travel much further" made a good trap. Brain fail.

E. When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal
background noise.  OK - that slow boat speeds do not kill any more than high boat speeds.

TooLong150 · Answer

MGMAT Explanation: https://www.manhattangmat.com/forums/pos ... 467#p98356

VarunBhardwaj · Answer

Premise 1: aquatic mammals are frequently killed in collisions with boats. 
Premise 2: manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows.
Conclusion: slowing the boat may in fact make things worse rather than better..........If the boat is slow, Manatees will not be able to hear the sound and will have more collsions.

A. The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported
collisions between manatees and boats.
 Incorrect: Our of scope.It doesn't matter how the speed of boat is defined. 
B. Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat
traffic.
 Incorrect: Our of scope.It doesn't matter how the speed of boat is defined. 
C. Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the
endangered manatee population.
 Incorrect:Although it is very tempting but the argument says   frequently killed in collisions with boat ,To address the problem  .So, we are only considered with mammals killed directly by collision. 
D. The sound of a boat engine generally travels much further under water than it does through the air.
Incorrect: Our of scope.It doesn't matter how much farther the sound travels in two mediums.
E. When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal
background noise.
 Correct: If manatees are not able to differentiate between the sound of high speed and the sound of low speed boat then slowing is NOT worsening the situation

Press Kudos if it helps.

nosaj · Answer

Sharing in case useful. I found it handy to RE-FRAME the conclusion.

"Therefore, this approach may in fact makes things worse rather than better".

"Therefore, this approach via reducing boat speed may in fact makes things worse because manatees can't hear low-pitched sounds from engines when they CAN today".

Answer choice E says that manatees can't discern sounds at any speeds. As a result, the conclusion does not make sense - they can't hear low pitched sounds nor high pitched sounds.

YuktiMaheshwari · Answer

GMATNinja  @karishma- Could please explain why not B? Because B also suggests that fast speed boats are causing harm, so eventually slow speed boats will aid in the manatee's survive.

GMATNinja · Answer

That's true: (B) gives us a reason why low boat speed is good for manatees -- it helps protect their food supply. However, it doesn't do anything to counter the author's argument. If the boats are moving at very low speeds, the manatees won't be able to hear the boats, and collisions might increase as a result.

Remember, the passage and the argument are only concerned with collisions with boats and what's currently being done to address that problem. The author is only interested in how the speed regulations will affect collisions. (B) is certainly relevant to a broader discussion, but (E) casts the most doubt on this specific argument and its conclusion.

I hope that helps!

Blackcrow1972 · Answer

Option D
This discusses the general travel of boat sounds but does not address whether manatees can hear the sounds at different speeds or how speed affects their safety.

Nsp10 · Answer

Conclusion:
new approach would not work
{What is the approach} ?
Boat is required to have slow speed, so Manatees won't die {means slow speed would not work}

we have to weaken this 
so we have to bring additional info such that this approach should work,

{how is it connected to the conclusion ?} {some prep companies call it the logical structure}
Manatees cannot listen to low sound and slow speed produces low sound.

Option B:
fast moving boats destroys Manatee's food.
{but we are concerned with how slow speed boat is causing or reducing the problem}

Option E:
The Manatees cannot differentiate the sounds irrespective of the speed of the boat.
so, if higher speed boat is producing more sound, then Manatee cannot listen to them and will get killed anyway,
but if speed is slower at least they can move aways from the boat and can survive, 
so here the approach may work unlike the conclusion

btsaami · Answer

Conclusion:  Lowering boat speed will not help in protecting mantees, rather it would make things worse.
 Premise:  Unfortunately, manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows
 Assumption:  Mantees rely on detecting boat sound and lowering the boat speed will have issue in sound detection which can cause accidents.
 Prethinking:  Option which undermines the above assumption, or which introduces another factor which implies that lowering boat speed might actually help in the protecting mantees.
 Why correct?  (E) When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal-background noise. --> This attacks the above assumption that manatees can recognize boat sound and react to it. If they cannot understand the boat sound, then lowering the boat speed will not worsen their ability to detect boat. Therefore, this will not worsen the situation. 
 Why wrong? 
(A) The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats. --> Decision might have taken by using the data, but it is irrelevant to whether lowering boat speed worsened or improved the situation.

(B) Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat traffic. --> Out of scope. Brings another factor for decline in mantees population, misses out on mantees accident with fast- and slow-moving boat.

(C) Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the endangered manatee population. --> This is just an extension of the premise and doesn't answer whether low speed boat can reduce accidents.

(D) The sound of a boat engine generally travels much further under water than it does through the air. --> If sound travel much further under water, then it should provide mantees enough time to escape with both high-speed and low-speed boat. No further information to determine whether it will make things worse with low speed boats. Hence, irrelevant.

Manatees, aquatic mammals inhabiting Florida’s rivers and coastal

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

Manatees, aquatic mammals inhabiting Florida’s rivers and coastal

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards