Before the age of space exploration, the size and composition of the m

Question

Before the age of space exploration, the size and composition of the moon's core were astronomical mysteries. Astronomers assumed that the moon's core was smaller than that of the Earth, in both relative and absolute terms — the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass — but they had no way to verify their assumption. However, data gathered by Lunar Prospector have now given astronomers the ability to determine that the moon's core accounts for 20 percent of the moon's radius and for a mere 2 percent of its overall mass.

The data have been used in two ways. In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a " gravity map " of both near and far sides of the moon. This map, in turn, revealed to scientists the distribution of the moon's internal mass. Scientists were then able to determine that the moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.

The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins. For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps as the result of a major asteroid impact. The impact could have loosened iron that had not already sunk to the core of the Earth, allowing it to form the core around which the moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by  so-called  centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.   1 
 D 
1. The primary purpose of the passage is best expressed as

(A) The author discusses the method of data utilization that proved that the moon was once part of the earth.

(B) The author discusses the methods of data utilization that changed scientists' opinions about the relative sizes of the earth's and moon's cores.

(C) The passage studies the method that, using data about radii and core mass, led to important implications about the origin of the planets.

(D) The passage studies the use of scientific methods to analyze data and confirm a hypothesis and references possible deductions.

(E) The passage discusses the implications following from the size of the Earth's core.

2 
 D 
2. According to the passage, scientists employed one research method that measured

(A) changes in a spacecraft's velocity as it returned to Earth

(B) changes in the gravitational pull on the Lunar Prospector as it orbited the moon

(C) changes in the moon's gravity as it orbited the earth

(D) changes in a spacecraft's radio signals as it changed position relative to the earth

(E) changes in the moon's gravitational pull over time

3 
 C

3. The author mentioned “ gravity map ” in the second paragraph in order to

(A) illustrate the method used to correct the Lunar Prospector’s velocity

(B) confirm the results obtained by examining the moon’s magnetic field

(C) detail a step in the investigation of the composition of a specific orbiting

(D) detail a step in the investigation of the effects of gravity on the moon and earth

(E) explain a step in the process of confirming a new hypothesis and discarding an older theory

4 
 A 
4. It can be inferred from the passage that

(A) the earth’s core contributes a higher proportion of both the earth’s total radius and its total mass than the core of the moon contributes to its own total radius and mass

(B) a comparison of the earth’s and moon’s cores suggests that the earth did break away from the moon

(C) scientists will eventually be able to use the gravity map to further the proof that a major asteroid impact caused the earth and moon to separate

(D) because the earth and moon were once joined, it is probable that scientists will eventually discover fossils and other evidence on the moon that indicates that a major asteroid impact caused the extinction of the dinosaurs

(E) the moon’s core has a higher ratio of iron in its composition than does the earth’s

5 
 B 
5. According to the passage, the magnetic field within the Moon’s core

(A) confirms the inconsistencies in radio signal wavelength detected by the Lunar Prospector

(B) is produced when the Moon moves through the Earth’s magnetosphere

(C) calls the results of the radio signal analysis into question

(D) permits the creation of a gravity map corresponding to lunar mass concentrations

(E) indicates the speed and direction of travel of the Moon

6 
 C 
6. If the wavelength of radio signals emitted by the Lunar Prospector were constant, then which of the following could be most properly inferred?

(A) The velocity of the spacecraft depends on whether it is on the near or far side of the Moon.

(B) The size and mass of the Moon’s core may be more comparable to the size and mass of the Earth’s core than is currently believed.

(C) As the craft orbits the moon, the Moon exerts a constant gravitational pull on the craft.

(D) The Earth and the Moon seem to have originated independently.

(E) It would be impossible to create a gravity map of the Moon.

7 
 E 
7. In the last sentence of the passage, the author uses the word “ so-called ” primarily in order to imply that

(A) the force may not have been adequate to cause the claimed ejection

(B) fission theory may have less explanatory power than impact theory

(C) the later coalescence of the Moon’s material may not have occurred as a result of centrifugal force

(D) the speed of the early Earth’s rotation may have led to the creation of the Moon

(E) the phenomenon in question might more properly be re-named

Manhattan CAT 3

carcass · Accepted Answer

1. 
The passage first talks about astronomers' assumptions regarding the earth's and 
moon's radii and core mass. The next two paragraphs detail the two methods 
astronomers employed to analyze their assumptions by using data collected by 
Lunar Prospector. The last paragraph discusses the implications of this data. 
(A) This choice founders over the use of the singular word "method" and the word 
"proved." There were two methods, and "proved" is too extreme. 
(B) This choice uses the word "changed," which is factually wrong because the 
passage says that it confirmed an assumption. 
(C) This choice fails because of the use of the singular "method," and because 
"planets" is too general for a passage only concerning the Earth and its moon. 
(D) CORRECT. It is acceptable to equate "implications" and "deductions," as well as 
"hypothesis" and "assumption." 
(E) This choice ignores the entire passage except for the last paragraph, and thus by 
definition can not be the passage's sum. 
 
2. 
The information to answer this question must come from the second or third 
paragraph. As it turns out, the choices all relate to the second one. The second 
sentence of that paragraph reads "measured minute variations in radio signals from 
Lunar Prospector as the craft moved towards or away from the Earth." 
 
(A) Changes in the craft's velocity were measured while the craft orbited the moon, 
not as A states as the craft "returned to Earth." 
 
(B) Although measurements of the Lunar Prospector 's velocity allowed scientists to 
create a "gravity map," the scientists did not measure directly the gravitational pull on 
the craft. 
 
(C) This choice is incorrect because the passage does not discuss changes in the 
moon's gravity. 
 
(D) CORRECT. The phrase "changed position relative to the earth" is a fair 
equivalent of "moved towards or away from the Earth." 
 (E) This choice is incorrect because the passage does not discuss changes in the 
moon's gravitational pull over time. 
 
3. 
This question asks why the author included this detail. The "gravity map" was a step 
in the determination of the size of the moon's core. We must find a choice that 
reflects this. 
(A) This choice is a distortion—the method was not used in this way. 
(B) This choice not only comes from the third paragraph but also reverses the 
relationship--the magnetic field work confirmed the map. 
(C) CORRECT. The author put in the detail to show a step in the investigation of the 
core ("composition") of the moon ("orbiting body"). 
(D) This choice contains the false word "earth"; in fact, the "moon" is the sole focus 
of the investigation of gravity's effects. 
(E) This choice incorrectly states that an older theory was discarded; in fact the old 
assumption was confirmed. 
 
4. 
Because the question is open-ended, the best approach is to evaluate the choices. 
 
(A) CORRECT. The information contained in A can be proven from the information in 
the passage. The ratios that it discusses can be found in the first paragraph: the 
earth's core contributes 55% of the earth's radius and 32% of its mass, compared to 
the moon's core contributing 20% of the moon's radius and 2% of its mass. Like 
many correct answers to inferences, the inference is very small. 
 
(B) This choice reverses the relationship suggested in the passage--that the moon 
might have broken away from the earth. 
 
(C) This choice does not have to be true both because said proof is not certain and 
because it is even less clear that the gravity map could be used for that purpose. 
 
(D) This choice is a typical GMAT flight of fancy that sometimes is given as a wrong 
choice; as dinosaurs are not mentioned at all, this answer is impossible. 
 
(E) This choice does not have to follow from the information provided. The passage 
does not give any information about the percentage of iron in the earth's core nor 
does it compare that aspect of the two cores.

NickHalden · Answer

My answers
1.D 2.E 3.C 4.B

carcass · Answer

Please provide explanations too

BillyZ · Answer

OFFICIAL EXPLANATION 
The context in which the author uses “so-called” is this: “the early Earth may have been spinning so rapidly that it ejected a quantity of material by so-called centrifugal force…” We need only focus on the final phrase, “so-called centrifugal force.” With “so-called,” the author indicates that, while some call the phenomenon “centrifugal force,” there may be another, perhaps better name.

(A) The term “so-called” specifically modifies “centrifugal force,” not “ejected.” The term does not imply that the force was insufficiently strong to eject a quantity of material.

(B) The two theories are not contrasted through the use of this word.

(C) According to the passage, the material “coalesced by mutual gravitational attraction,” not centrifugal force. The ejection of the material apparently occurred by “so-called centrifugal force.”

(D) The theory does indicate that the speed of the Earth’s rotation may have led to the creation of the Moon, but the term “so-called” modifies only the term “centrifugal force.” It does not address the overall theory.

(E) CORRECT . The phenomenon in question is “centrifugal force” and the description “so-called” implies that the term centrifugal force might not be the most proper name or description of what is occurring.

jawele · Answer

2. According to the passage, scientists employed one research method that measured
(D) changes in a spacecraft's  radio signals  as it changed position relative to the earth

I'm a bit confused about D here. The original passage uses '  rapid variations in the wavelength of radio signals from Lunar Prospector   Could anybody please explain me why 'radio signals' are correct although the passage claims that the scientists measured 'the wavelength of radio signals'. I would understand the scientist measured changes in the length of certain radio signals. This is different from changes in 'radio signals', i.e. changes that result in different signals: from Signal 1 to Signal 2, etc.

I'm a little bit lost here: perhaps it's physics that I don't understand.

Thanks

Prateek176 · Answer

carcass  ,  hazelnut

I still didn't understand the explaination for Q.7.

Adi93 · Answer

hazelnut

If you have OE for Question 6, please post it.

oasis90 · Answer

I think question 7 is the weirdest question I have ever seen on the GMAT. Never seen anything like it on the actual GMAT or GMAT Prep or anything official. If you still don't get it, don't fuss much over it. it's very atypical.

avocado310 · Answer

The passage implies which of the following about the scientists’ research of the Moon’s core?

A. The Earth's core contributes a higher proportion of both the Earth's total radius and its total mass than the core of the Moon contributes to its own total radius and mass.

B. A comparison of the Earth's and the Moon's cores suggests that the Earth did break away from the Moon.

C. Scientists will eventually be able to use the gravity map to further the proof that a major asteroid impact caused the Earth and the Moon to separate.

D. If the sizes of the Earth’s and Moon’s cores were more comparable, then scientists would conclude that they had developed as distinct entities.

E. The Moon's core has a higher ratio of iron in its composition than does the Earth's.

I ended up picking the right answer, but am having a hard time understanding the explanation for why D is wrong. I accidentally misread the passage and thought that the sentence was comparing the "mass of their cores" vs the size and removed it.

Response provided: (D) The passage says that “if the Moon and Earth developed as distinct entities, the sizes of their cores should be more comparable.” We cannot simply reverse that relationship to claim that, if the cores were “more” comparable than they are today, then scientists would be able to conclude that the two entities definitively developed separately.

gmatconqueror2018 · Answer

6/7 in 13:37

4/4 in 8:18 on first 4 questions. Interesting read with quite a few tough questions. Got the last one wrong. Was really hard to be sure what the purpose of "so-called" was. Would love to hear an explanation. Besides that, other questions very realistic to GMAC questions. The level of difficulty on this passage is more 600 or 700 level? I thought the passage itself was medium, but the questions were on the upper end.

mimishyu · Answer

para1
how the age of space exploration open the inquiry into moon’s core to which we use data of radius and mass of earth to compare to moon’s

para2
by using data mention in para1 we could derive two methods applied

para3 
how the implication to the data concern with composition of moon’s core lead to our better understanding of moon’s origin
---->
(1)impact theory --->moon was once part of the earth, broke away ….as a result of a major asteroid impact
(2)fission theory ---> earth’s centrifugal force that coalesce by mutual gravitational attraction into the Moon

mimishyu · Answer

1. The primary purpose of the passage is best expressed as

I was confused between (C)&(D) at first, thanks to carcass’s explanation now I know where my crux is

(A) The author discusses the method of data utilization that proved that the moon was once part of the earth.

…incorrect
“moon was once part of the earth”…this only appear in para3, thus cannot be the primary purpose

(B) The author discusses the methods of data utilization that changed scientists' opinions about the relative sizes of the earth's and moon's cores.

…incorrect
opinions about relative sizes of the earth's and moon's cores….this only appear in para1

(C) The passage studies the method that, using data about radius and core mass, led to important implications about the origin of the planets.

…not as best as (D)
studies the method….. the passage concern with two methods rather than one, I didn't notice this subtlety at first

the origin of the planets: here we only concern about the moon’s origin 
The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins.

(D) The passage studies the use of scientific methods to analyze data and confirm a hypothesis and references possible deductions.

…correct

the explanation:
(D) CORRECT. It is acceptable to equate "implications" and "deductions," as well as 
"hypothesis" and "assumption."
……….I cannot get its meaning very well

hypothesis:
see para2, last sentence ---
This approach confirmed the results obtained through examination of the gravity map….this is hypothesis

references possible deductions:
para3 ---
The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins....so para3 is about the deduction to the composition of moon's core which produce two theories to the moon's origin

(E) The passage discusses the implications following from the size of the Earth's core.
…out of scope

2. According to the passage, scientists employed one research method that  measured
 
(A) changes in a spacecraft's velocity as it returned to Earth

(B) changes in the gravitational pull on the Lunar Prospector as it orbited the moon

(C) changes in the moon's gravity as it orbited the earth

(D) changes in a spacecraft's radio signals as it changed position relative to the earth
…correct, see sentence in para2 below:

The data have been used in two ways. 
In the first method, scientists  measured   minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth.  These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a "gravity map" of both near and far sides of the moon.
The second method involved examining the faint magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere.

(E) changes in the moon's gravitational pull over time

3. The author mentioned “gravity map” in the second paragraph in order to

(A) illustrate the method used to correct the Lunar Prospector’s velocity. ….out of scope

(B) confirm the results obtained by examining the moon’s magnetic field. ….out of scope

(C) detail a step in the investigation of the composition of a specific orbiting 
…correct

(D) detail a step in the investigation of the effects of gravity on the moon and earth
…incorrect
(E) explain a step in the process of confirming a new hypothesis and discarding an older theory. 
…out of scope

See 
para1
before the age of space exploration,  the size and composition of the moon's core  were astronomical mysteries.

&para2
In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the  Earth . These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the  moon . These changes resulted from inconsistency in the gravitational pull of the  moon  on the craft, and permitted scientists to create a " gravity map " of both near and far sides of the  moon .

….here the gravity map is only concerned about "the Moon"

This question asks why the author included this detail. The "gravity map" was a step in the determination of the size of the moon's core. We must find a choice that reflects this. 
(A) This choice is a distortion—the method was not used in this way. 
(B) This choice not only comes from the third paragraph but also reverses the 
relationship--the magnetic field work confirmed the map. 
 (C) CORRECT. The author put in the detail to show a step in the investigation of the core ("composition") of the moon ("orbiting body"). 
(D) This choice contains the false word "earth"; in fact, the "moon" is the sole focus of the investigation of gravity's effects.

….earth is only used as supplement to compare for moon
(E) This choice incorrectly states that an older theory was discarded; in fact the old assumption was confirmed.

4.It can be inferred from the passage that

(A) the earth’s core contributes a higher proportion of both the earth’s total radius and its total mass than the core of the moon contributes to its own total radius and mass

….correct, see para1:
Astronomers assumed that the moon's core was smaller than that of the Earth, in both relative and absolute terms — the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass — but they had no way to verify their assumption. However, data gathered by Lunar Prospector have now given astronomers the ability to determine that the moon's core accounts for 20 percent of the moon's radius and for a mere 2 percent of its overall mass.

(B) a comparison of the earth’s and moon’s cores suggests that the earth did break away from the moon.

…..incorrect

For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that  the moon was once part of the Earth and broke away at an early stage in the Earth's evolution , perhaps as the result of a major asteroid impact.
---thus it should be "moon break away from earth"

(C) scientists will eventually be able to use the gravity map to further the proof that a major asteroid impact caused the earth and moon to separate.

….incorrect
...nowhere in the passage mention about this

(D) because the earth and moon were once joined, it is probable that scientists will eventually discover fossils and other evidence on the moon that indicates that a major asteroid impact caused the extinction of the dinosaurs.

….totally out of scope

(E) the moon’s core has a higher ratio of iron in its composition than does the earth’s.

….the passage doesn’t intend to compare the ratio concerned with iron

The impact could have loosened iron that had not already sunk to the core of the Earth, allowing it to form the core around which the moon eventually coalesced(merge).

5.According to the passage, the  magnetic field  within the Moon’s core

(A) confirms the inconsistencies in radio signal wavelength detected by the Lunar Prospector

….out of scope
….this sentence concern with the first method rather than second method

(B) is produced when the Moon moves through the Earth’s magnetosphere

….correct
….see para2:
The second method involved examining the faint  magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere.  This approach confirmed the results obtained through examination of the gravity map.

(C) calls the results of the radio signal analysis into question

call into question….wrong, the author never call radio signal analysis into question, rather, he “confirmed” the results obtained through examination of the gravity map(the first method)

(D) permits the creation of a gravity map corresponding to lunar mass concentrations….out of scope

gravity map….is for first method, thus out of scope

(E) indicates the speed and direction of travel of the Moon
….out of scope

6.If the wavelength of radio signals emitted by the Lunar Prospector were constant, then which of the following could be most properly inferred?

In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a "gravity map" of both near and far sides of the moon.

(A) The velocity of the spacecraft depends on whether it is on the near or far side of the Moon.

….incorrect, the passage never mention anything about the relation of the velocity of spacecraft to the Moon

variation in radio signals(wave length)
--> inconsistency in the gravitational pull 
and we only know that the above will lead to
--> permitted scientists to create a "gravity map" of both near and far sides of the moon.

However,
constant in radio signals(wave length)
-->
its insufficient to determine whether this
-->”cannot” permit scientists to create a "gravity map" of both near and far sides of the moon….option(E)
or
“the velocity of the spacecraft depends on whether it is on the near or far side of the Moon”

(B) The size and mass of the Moon’s core may be more comparable to the size and mass of the Earth’s core than is currently believed.

….out of scope

The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins. For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. I
….this concern with para3
 
however, what this question ask is in para2

(C) As the craft orbits the moon, the Moon exerts a constant gravitational pull on the craft.

…correct

see sentence below: 
scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft,……..
…..variation in radio signals(wave length)-->inconsistency

so if “the wavelength of radio signals emitted by the Lunar Prospector were  constant ”(opposite to what the passage says), 
--->>
then “the Moon must exerts a  constant  gravitational pull of the moon on the craft”

(D) The Earth and the Moon seem to have originated independently. 
….out of scope

(E) It would be impossible to create a gravity map of the Moon.
….incorrect, I’ve already explained in option(A)

sarphant123 · Answer

carcass  Please correct the option C in the Problem 3.
"From specific orbiting" to "specific orbiting body"

aditiphadnis · Answer

Looks like a very difficult passage. It was easy to understand but questions were super difficult. I Got all wrong. This doesn't usually happen. Is this 800 level passage?

Sajjad1994 · Answer

This is a medium to hard (650) level passage.

Thanks

Mavisdu1017 · Answer

hello expert,
can any expert help on Q6? I think both C and E are correct.
As passage says: inconsistency in the gravitational pull of the moon on the craft permitted scientists to create a "gravity map", so I think if radio signals are constant, then can't create a gravity map. 
Could you explain why E is not correct? Thanks

Sajjad1994 · Answer

Follow the post in the link below for explanation to question #6. https://gmatclub.com/forum/before-the-a ... l#p2499285 Cheers

Mavisdu1017 · Answer

Thanks for your response. I have seen it, but it is not convincing and does not address my question, so I asked for an expert.

Sourav04 · Answer

3 / 7 I got 2 question wrong bcoz of lack of focus May be.

Before the age of space exploration, the size and composition of the m

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 Reading Comprehension (RC) Questions

Before the age of space exploration, the size and composition of the m

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