GMAT Prep tough RC

[akhpad]

Although this is a short passage, it seems to be very hard for me. Can you please explain?

When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clemenstine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.

According to the passage, the gravitational compensation referred to in the highlighted text is caused by which of the following?
A) A deficit of mass resulting from the creation of hole in lunar surface
B) The presence of material from the impactor in the debris created by its impact
C) The gradual cooling and stiffening of the Moon's outer surface
D) The ejection of massive amounts of debris from the moon's crust
E) The rapid upwelling of material from the lunar mantle
OA: E

The Passage suggests that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
A) were not formed early in the Moon's history
B) were not formed by the massive ejection of crustal debris
C) are closely surrounded by other impact basins with anomalously low gravity
D) were created by the impact of multiple large impactors
E) were formed when the moon was relatively elastic
OA: A

The passage is primarily concerned with
A) analyzing data from a 1994 exploration of lunar surface
B) reconciling two opposing theories about the origin of lunar impact basins
C) presenting a possible explanation of a puzzling finding about lunar impact basins
D) discussing how impact basins on the Moon's surface are formed
E) examining the claim that the moon's impact basins show negative gravity anomalies
OA: C

[Shawshank]

PLEASE PUT a spoiler on the answers,,,, how do u expect people to try whne u have mentioned the answers right below the question ,,, without spoilers..

[beat_gmat_09]

Although this is a short passage, it seems to be very hard for me. Can you please explain?

When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clemenstine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.

According to the passage, the gravitational compensation referred to in the highlighted text is caused by which of the following?
A) A deficit of mass resulting from the creation of hole in lunar surface
B) The presence of material from the impactor in the debris created by its impact
C) The gradual cooling and stiffening of the Moon's outer surface
D) The ejection of massive amounts of debris from the moon's crust
E) The rapid upwelling of material from the lunar mantle
OA: E

The Passage suggests that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
A) were not formed early in the Moon's history
B) were not formed by the massive ejection of crustal debris
C) are closely surrounded by other impact basins with anomalously low gravity
D) were created by the impact of multiple large impactors
E) were formed when the moon was relatively elastic
OA: A

The passage is primarily concerned with
A) analyzing data from a 1994 exploration of lunar surface
B) reconciling two opposing theories about the origin of lunar impact basins
C) presenting a possible explanation of a puzzling finding about lunar impact basins
D) discussing how impact basins on the Moon's surface are formed
E) examining the claim that the moon's impact basins show negative gravity anomalies
OA: C

My Road map for this passage -
Large body -> strikes -> ejects material & creates hole.
Mass loss = impact in gravity, less gravity at hole.
Expectation Multi ring -> very large body impact shows gravity anoml.
But (Crucial to above theory) - 1994 study -> variation in gravity.
Speculation to 1994 study - large impact; displacement in mass underlying large object (Ques 1)= Compensation + no gravity anoml.
Moon-> Cool+less elastic = no displacement of mass.
Today = No compensation, moon outer surface = too cold + stiff.

1) Compensation -> caused by Upswelling - Option E.
A - deficit is in the theories claim. Starting explanation of theory, which explains displacement not compensation.
B - Object's debris are nowhere discussed.
C - Cooling and Stiffening is discussed lately (Today), compensation happens/caused because of moons surface displacement.
D - Ejection again discussed in starting of explanation of the theory.

2) I choose E, didn't understand the OA.
Please post the explanation, if you have.

3) Primary Purpose -
A - Passage is not limited to 1994, instead theory's year is not mentioned, Today is mentioned.
B - There is only one theory - Gravity anomaly, on which speculations are done to resolve paradox. No new theory is proposed.
C - To be kept. Passage is focused on explaining why was the theory unproven in 1994 findings, possible explanation by the scientists and supporting point at Present day.
D - Passage is concerned with Gravity not impact of basins.
E - Passage does not discuss only negative anomalies.

Please use spoilers for OA.
Thanks

[GMATGuruNY]

Although this is a short passage, it seems to be very hard for me. Can you please explain?

When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clemenstine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.

The italics indicate words quoted directly from the passage:

According to the passage, the gravitational compensation referred to in the highlighted text is caused by which of the following?
A) A deficit of mass resulting from the creation of hole in lunar surface
B) The presence of material from the impactor in the debris created by its impact
C) The gradual cooling and stiffening of the Moon's outer surface
D) The ejection of massive amounts of debris from the moon's crust
E) The rapid upwelling of material from the lunar mantle ...denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity.

The Passage suggests that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
A) were not formed early in the Moon's history early in lunar history...no gravity anomaly in the resulting basin.
B) were not formed by the massive ejection of crustal debris
C) are closely surrounded by other impact basins with anomalously low gravity
D) were created by the impact of multiple large impactors
E) were formed when the moon was relatively elastic
OA: A

The passage is primarily concerned with
A) analyzing data from a 1994 exploration of lunar surface
B) reconciling two opposing theories about the origin of lunar impact basins
C) presenting a possible explanation of a puzzling finding about lunar impact basins One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies...yet many of these Clementine basins have no anomalously low gravity. Scientists speculate...
D) discussing how impact basins on the Moon's surface are formed
E) examining the claim that the moon's impact basins show negative gravity anomalies

[lunarpower]

hi --

rather than just spitting out answers, i'll try to give some strategies that you can employ in the future, based on key words in the problem statements/prompts.

1st question:

According to the passage, the gravitational compensation referred to in the highlighted text is caused by which of the following?

whenever you see "according to the passage", you know that you are looking for material that is EXPLICITLY GIVEN in the passage.
there will usually be minimal, if any, rephrasing of that material; the primary danger in many incorrect answers is that they contain words quoted from the passage, but mixed up in ways that make them false (misquotations).

especially in science passages, the answers to "according to the passage" questions will basically be repetitions (almost verbatim) of the information in the passage.

... so, go find the word "compensation" (or "compensatory", or "compensate", or some other word of that sort), and then go find the most proximately supplied reason.
you'll get the correct choice (e).

[lunarpower]

2nd question:

The Passage suggests that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably

IN EVERYDAY CONVERSATION, "suggests" is a very vague-sounding word; usually, it is taken to mean that the reader or listener should take the aggregate of the information supplied, and take his/her best guess at some sort of (relatively random) conclusion.

this is the reason why these questions are so difficult on RC: the word "suggests" (also also similar words, such as "inferred") signifying something completely different.
on the gmat, a "suggestion" or "inference" is something that MUST be true, based on the information in the passage.
notice -- "MUST".
not just "probably true", not just "vaguely suggested"... but "MUST be true".
as a result, the answers to inference or suggestion problems will usually be (a) rather boring and unambitious, and (b) VERY closely related to the information already given in the text.

part (b) here is no joke -- it's not uncommon to see passages that say "x is less than y", for which the answer to an inference question is "y is more than x". seriously. (this is basically what happens in OG12 rc problem 74, for instance)

so, basically --

* go find information about these "speculations"
* go find a choice that says, as closely as possible, EXACTLY what is said in the passage (though phrased somewhat differently).

the passage says:
Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin.

so ...
"EARLY in the moon's history --> you get no gravity anomaly"

this is pretty much exactly the same thing as saying
"if you get a gravity anomaly --> it wasn't early in the moon's history"
(if you're a big formal logic person, this actually is exactly the same statement -- this is known as the "contrapositive transformation", although it's clearly unnecessary to think about such things explicitly)

so ...
A) were not formed early in the Moon's history

[lunarpower]

question #3:

The passage is primarily concerned with

this is a MAIN IDEA question.

if you notice a MAIN IDEA question, your best bet is to:
* COVER the choices (yes, physically ... with your hand or notepad) before looking at them
* PREDICT the answer
* CHECK
otherwise, it's easy to be led astray by tempting, but wrong, answer choices.

if you have trouble doing this -- i.e., if you naturally have a very detail-oriented disposition, and generally have trouble "grasping" main ideas in passages across the board -- then you can always try just eliminating choices containing things that don't appear in the passage.
for instance:

A) analyzing data from a 1994 exploration of lunar surface

the passage doesn't contain any "data" -- just generalizations. ("Data" generally refers to numerical statistics.)
so, auto-wrong.

B) reconciling two opposing theories about the origin of lunar impact basins

the passage contains only one theory -- that of the scientists. ("One would expect..." is NOT a theory.)
so, auto-wrong.

C) presenting a possible explanation of a puzzling finding about lunar impact basins

yep.

D) discussing how impact basins on the Moon's surface are formed

this is in the passage, but it's not the main focus; it's a background fact.

E) examining the claim that the moon's impact basins show negative gravity anomalies

to "examine a claim" is to QUESTION whether it is right or wrong. that doesn't happen here; the FACT that the moon's impact basins show negative gravity anomalies is ... well, a FACT.

[ankurmit]

For quistion 1:

I am confused between D and E. Both seems correct.

Ron you have selected D as answer but OA is E.
please guide.

[lunarpower]

For quistion 1:

I am confused between D and E. Both seems correct.

Ron you have selected D as answer but OA is E.
please guide.

yeah, made a typo there. that seems to happen a lot when i do threads with multiple questions.

fixed. thanks.

[[email protected]]

Hi Ron,
I understand why A is a good answer since the passage specifically cites "early in lunar history," but why not option E "were not formed when the moon was relatively elastic." The passage goes onto say "later, as the moon grew cooler AND LESS ELASTIC, rebound from large impactors would have been only PARTIAL AND INCOMPLETE."

Quick response appreciated. Thanks!

[lunarpower]

Hi Ron,
I understand why A is a good answer since the passage specifically cites "early in lunar history," but why not option E "were not formed when the moon was relatively elastic." The passage goes onto say "later, as the moon grew cooler AND LESS ELASTIC, rebound from large impactors would have been only PARTIAL AND INCOMPLETE."

yeah -- that's why this answer choice is exactly the opposite of what you want.

read the surrounding part again; "rebound from large impactors" is actually what prevents the gravity anomalies from forming (by basically straightening everything back out again).
more directly, "early in lunar history ... leaving no gravity anomaly in the resulting basin".
so, this is the time in history that you don't want.

Quick response appreciated.

please don't do this. it's unprofessional and somewhat rude -- and it definitely won't produce faster responses.

[mithelash]

The Passage suggests (infer) that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably

A) were not formed early in the Moon's history
B) were not formed by the massive ejection of crustal debris
C) are closely surrounded by other impact basins with anomalously low gravity
D) were created by the impact of multiple large impactors
E) were formed when the moon was relatively elastic
OA:A

. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin

Sci (early) = some stone hit = some area is ejected + some area is up( as a comp) + no gravity change.

Q : if the highlighted text are correct(Sci (early) = some stone hit = some area is ejected + some area is up( as a comp) + no gravity change.)
the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably (if it has gravity change what will be true)


If gravity is changed its not happened in early (frm sctst speculation)

Ans: were not formed early in the Moon's history

[vjns]

Hi Ron,
I am still not able to understand why E is not a possible answer. Though I am convinced that A is a better choice as it is direct opposite of what is mentioned in the passage, I want to understand why E is incorrect.

"Scientists speculate...resulting basin." - Earler, large impactors caused holes, but denser mantle material refilled the -> no low gravity anamoly.
"Later...cold and stiff." - Later moon cooler + less elastic (stiff) -> filling of holes partial -> no gravitational compensation.

From the second quoted text can we not derive that the holes were formed when Moon was cooler and stiff?

Could you please help me understand better? In the absence of A, would E be the correct answer?

[lunarpower]

Choice E talks about a time when the moon was "relatively elastic".

The "Later" part (that you're citing) is when the moon was "less elastic" -- i.e., a time that's irrelevant to choice E.

Could you please help me understand better? In the absence of A, would E be the correct answer?

Answer choices aren't affected by other answer choices. Four are wrong; one is right.

[buoyant]

Hi Ron,

I am not able to understand why the answer choice B is incorrect in question #2 ?

Can't this be inferred from the below portion in the passage :
"This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas."

i.e when debris are ejected,holes with negative gravity anomalies are formed in moon surface...

Could you please explain?