In order to withstand tidal currents, juvenile horseshoe

i am still not able to stand why E is correct answer.the statement E have same effect whether horseshoe crabs stay in strong tide current region or weak tide current region.how it explain the low population of barnacle in weak tidal current area.

This is a Resolve the paradox Question.The Paradox is when the tides hit the Adult Crabs there will be barnacles attched to them But in weak tide (this is a decoy)areas even though the tides hit Juvenile crabs there are not more barnacles.The correct ans choice must allow both the facts to be true and explain the paradox.Only Option E tells how the Juveniles shed the shell and hence have no barnacles if Adults they wud have had clusters of Barnacles too

This is an Explain the Paradox question type!

Premises:
- juvenile horseshoe crabs frequestly burrow in sand to withstand tidal currents
- burrowing discourages barnacles from clinging to juvie's shells
- fully grown horseshoe crabs can readily withstand tidal currents without burrowing and therefore acquire substancial populations of barnacles

Conc:
- in areas where tidal currents are weak, juvenile horshoe crabs found not ot have significant barnacle populations, even though theyy seldom burrow

a) we already know that BURROWING does. this does not explain anything.
b) then there should be MORE barnacles on their shells.. opp direction
c) tempting but doesn't FULL explain... what is the range of this strength? doesn't really answer our discrepancy
d) out of scope.
e) bingo! if horse shoe crabs are shedding their shells and growing new ones, this w ould explain why we didnt find significant barnacles on their shells even though they weren't burrowing.

Answer is E

I had a really hard time understanding Choice A. I'm wondering if my thought process is correct in disqualifying A now.

Here's how I understand the argument:
- high tidal waves --> more burrowing for juvenile horseshoe crabs --> decreased barnacles
BUT ALSO
- low tidal waves --> less burrowing for juvenile horseshoe crabs --> decreased barnacles
how can this be?

A. Tells us that the water tides don't matter. So the less or more barnacle populations have to do with burrowing then (given the premises). So we are left with the situation where:
- more burrowing --> less barnacle population
- less burrowing --> less barnacle population
So...we still have a paradox.

Is this accurate?

Let me take a dig at trying to explain the answer choice.

Choice A says that the tidal ways do not dislodge the barnacles from the crab-shells. Thus high or low tidal waves should not make a difference in the population of barnacles, instead burrowing should make all the difference i.e. less burrowing = more barnacles and vice-versa.

Hence in low tidal waves areas the juvenile crabs would burrow less hence ideally the population of barnacles on the juvenile crabs should be larger. However this is contrary to the observed phenomenon i.e. in low tidal areas the barnacle population on juvenile crabs was not found to be larger. Thus option A does not help us resolve the paradox. Hence A can be eliminated.

Hope this helps.

My 2 cents:

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells.
When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles.
Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?
[Solve the paradox]
(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
>>Evident from argument "burrowing discourages barnacles from clinging". Doesn't help in answering the paradox.
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
>>But juvenile horseshoe crabs are found not to have significant barnacle populations in such areas. Doesn't help.
(C) The strength of the tidal currents in a given location varies widely over the course of a day.
>> I found this one intriguing. but this means Barnacle population shouldnt vary much because of variation in tidal strength.
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.
>>Irrelevant.
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.
>>Now apart from sand borrowing this is anther reason for low barnacle population. This answers bth part of argument.

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

The question to answer is, why do juvenile horseshoe crabs have sparse barnacle populations although they aren't burrowing (Burrowing decreases barnacle accumulation)?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs. doesn't answer the question
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest. This would have the opposite effect.
(C) The strength of the tidal currents in a given location varies widely over the course of a day. not relevant to our question
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food. also out of scope
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year. This explains why they don't have barnacles although we would think they would because they don't burrow. They shed the barnacles along with their shells.

OFFICIAL EXPLANATION:


Argument Construction

Situation - Juvenile horseshoe crabs withstand tidal currents by burrowing in the sand.
This action makes barnacles less likely to cling to their shells. Adult horseshoe crabs can
withstand currents, so they do not burrow, and barnacles become more likely to cling to
their shells. Surprisingly, however, juvenile horseshoe crabs that do not burrow, because
tidal currents do not threaten them, do not have significant numbers of barnacles clinging
to their shells.

Reasoning - What would most help explain the finding that nonburrowing juvenile
horseshoe crabs do not have significant barnacle populations? The finding suggests that
there is some way in which nonburrowing juvenile horseshoe crabs either discourage
barnacles from clinging to their shells, or get rid of the barnacles that do cling to their
shells. Identifying how this is accomplished will explain the finding.

A. This gives a reason why juvenile horseshoe crabs that do not burrow would have
significant barnacle populations.

B. If barnacles in areas of weak tidal currents readily attach themselves to horseshoe
crabs, then it would be more likely for juvenile horseshoe crabs in such areas to
have significant barnacle populations.

C. The areas under discussion are those where tidal currents are very weak. The
strength of currents may vary widely there, but presumably they are still weak
compared to other areas.

D. The surprising finding under discussion is why certain juvenile horseshoe crabs do
not have significant barnacle populations, despite failing to engage in behavior that
dislodges barnacles. That a very large barnacle population can hurt a horseshoe crab
does not help explain such a finding.

E. Correct. This statement properly identifies something that helps explain the
surprising finding: If juvenile horseshoe crabs regularly shed their shells, they also
regularly shed the barnacles that cling to those shells. Thus juvenile horseshoe
crabs would most likely be found not to have significant barnacle populations.

The correct answer is E.

I see every one simply eliminate (D), saying it’s our of scope.
However, isn’t there possibilities that the reason crabs that lives at the waek tidal currents are found not to have significant populations of barnacles because crabs who have significant populations of barnacles are all already dead.
The tidal currunts are very weak so more barnacles can cling to cabs than do normal tidal currents thus they can’t eat so they are dead.

Can someone explain me this please?

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In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Surprising finding: on juvenile crabs, significant barnacle populations are not found. To explain this finding, a connection between juvenile crab and lack of observable barnacle in areas with weak tidal current should be established

Which of the following, if true, most helps to explain the surprising finding?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs. Nothing relevant
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest. This one makes the finding even weirder as there should be more observable barnacles
(C) The strength of the tidal currents in a given location varies widely over the course of a day. so what?
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food. not relevant to the finding
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year. yes. Juvenile = not fully grown. This answer says that young crab shred their shells several times, so barnacle could not stay on for long

In Paradox question, we need to find an option that explain /connect both sides of paradox.
In 4 options, it would explain only 1 side; the other side wouldn’t be valid

In this question two sides are:

One side: burrowing discourages barnacles from clinging to their shells.
Opposite side: found not to have significant barnacle populations, even though they seldom burrow.

Can D explains reasoning of both sides?


Ask yourself: ability to find food has any relation with barnacle population sting to its wings ? barnacles clings to its wings ; not crab ask them to cling to its wings or use its ability to make them cling to its wings.
So ability discussion is irrelevant from our point of concern.
What about : A very large barnacle population?
If a large population then more barnacles should stick to its wings. But it doesn’t explain why barnacles don’t stick in weak currents even curbs don’t borrow. So this option only explains one side.It doesn’t explain reasoning of opposite side .


As per our argument, we stay in the scope what is mentioned
Our scope of argument is : Barnacles cling in scenario. But found not cling even scenario is favorable. This can happen only when some new factor connects these 2 sides. What will happen in future, they are dead etc. will be out of scope for this argument.

GMATNinja

Wouldn't you have to know that barnacles permanently attach to the shell to answer this question? I don't think the words "cling" and "adhere" can infer that the barnacles are permanent. Couldn't they technically "cling to"/"adhere to" the shell only during the tidal currents?

Please let me know if I'm missing something.

ef1988
The text tells us that adult horseshoe crabs acquire "substantial populations" of barnacles, so that tells us that it isn't just a temporary phenomenon, like flies on cattle. E gives us a reason that juveniles would be different from adults, so it helps clear up the mystery. But sure, having said all that, it helps to know what barnacles are. Although the GMAT will usually explain needed vocabulary words, we may need to lean on our own knowledge when no explanation is given.

I am not satisfied by answer E. (though no other option is as promising as E).
To all those who are saying E, please explain to me how it solves paradox? suppose if we compare an adult in high tide and an adult crap in low tide. then why does the crab in low tide have lower barnacles? crab has already become mature/adult. leaving skin etc mattered till it becomes adult. But then after it becomes an adult, what happens? why less population of barnacles on adult crap in the low tide?

it's very simple. Because they shed old skin and grow new ones. What does it mean?
Old skin may had lot of barnacles . but at new skin in the beginning this new skin may not have lot of barnacles .
this bridges the gap.
in places whereever weak tides then barnacles cling to skin but because matured crab shed their skins, so you don't find many barnacles even at weak current places.

C is a trap answer that is very mind-boggling.
The explanation for why C is not the answer.

"Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow."
--> The surprising finding is that these very juvenile horseshoe crabs don't have significant barnacle populations (like their fully grown brothers?) in areas of very weak tidal currents. They even seldom burrow in the sand.

"In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand." --> the juvenile crabs only "withstand tidal currents" if these currents are strong. They don't have to deal with the weak tidal currents and therefore, seldom burrow in the sand.

C. The strength of the tidal currents in a given location varies widely over the course of a day.
Assuming that "varies widely" means the currents can be strong and then "very weak", when the currents are strong, the juvenile horseshoe crabs will definitely burrow in the sand. Since the answer says "over the course of a day", the crabs have to burrow in the sand every single day, which contrasts with "they seldom burrow" at the end of the text. And the case of strong currents is not really valid because the text already says "in areas where tidal currents are very weak".

It leaves us with the assumption that "varies widely" means having a wide range of different weak tidal currents. Throughout a day, the juvenile crabs might acquire a small number of barnacles since the water is so weak that it cannot bring a lot of barnacles to the shore. This will answer the question of why it is surprising that the juvenile crabs don't have significant barnacle populations. However, another scenario is the juvenile crabs might acquire a significant amount of barnacles because even though the currents are weak, there are a lot of barnacles in the water. So we are unsure of the number of barnacles that the juvenile crabs acquire.

If I have to do a painstaking analysis for this answer, this answer is not the correct answer. The right answer tends to be more straightforward and very comprehensive so once you choose it, you have a gut feeling that it's correct. I don't mean that we guess based on our feelings. I have total belief in reading the text carefully and choose an answer based on the text.

This trap answer will waste most of our time and from time to time, I still have the thinking that oh, there is something about it that makes it correct

uttonio
I'm not sure we need to do that much analysis to cut C. The argument states that the juvenile crabs in these areas seldom burrow AND don't have significant barnacle populations. Since the strength of the tide was only discussed as the reason for burrowing, and we know that not much burrowing is occurring here, there's nothing further we can do with the information in C. As you've surmised, any variation we do see is clearly not enough to cause much burrowing. We can't speculate about any other possible results of this variation, since we haven't been given any means to do so. So we should toss this out as a "variation trap" and move on. The GMAT loves to get us wondering about some difference that we don't have the information to assess. As you've said, we shouldn't fall for the trap and use up our time!