A meteor stream is composed of dust particles that have been ejected

Question

A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time.  Conventional theories , however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.   1 
 1.The primary focus of the passage is on which of the following?

(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data

2 
 2. According to the passage, which of the following is an accurate statement concerning meteor streams?

(A) Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.
(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.
(C) Meteor streams are composed of dust particles derived from comets.
(D) Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.
(E) Once formed, meteor streams hasten the further disintegration of comets.

3 
 3. The author states that the research described in the first paragraph was undertaken in order to

(A) determine the age of an actual meteor stream
(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data

4 
 4. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?

(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.

5 
 5. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?

(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.

6 
 6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?

(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

7 
 7. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

(A) Most meteor streams it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
(D) It usually takes over a day to cross the actual Geminid meteor stream.
(E) It accounts for most of the gravitational perturbation affecting the Geminid meteor stream.

8 
 8. Which of the following is an assumption underlying the last sentence of the passage?

(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
(D) The Geminid meteor stream has not broadened as rapidly as the conventional theories would have predicted.
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.

DmitryFarberMPrep · Accepted Answer

8. Which of the following is an assumption underlying the last sentence of the passage? It's safe to say that if you are thinking about the possible destruction of the Earth, you have strayed too far from the text!

As in a CR assumption question, we want something that bridges the conclusion at hand with other information provided directly in the passage. One way to test our answers is to apply the Negation Test. If we negate the text in a particular answer choice and that poses a problem for the argument, then we have found a necessary assumption. If it doesn't, then we can cross that answer out. Let's try. First we need to keep in mind what conclusion we're dealing with. The last line says that the stream is about 3,000 years old. Why does the author think so? Because of the time it takes to get from one burst of meteor activity to the other. How can we connect the distance between the edges and the age of the stream? With the earlier information about the development of the stream over time. The conventional theories say that the stream should get dense in the center, while the computer model predicts a shape more like the hollow pipe. The observations in the last paragraph seem to match the computer model, so the author figures that we can use that model to determine how long the stream took to get this way. Now let's look at how each answer choices relates once we negate: (A) The Earth did not take exactly 19 hours to cross each year. This is fine. In fact, the passage makes it clear that the time should vary from year to year. 19 hours is just an average. Eliminate. (B) The comet has not totally disintegrated. Well, what do we mean by totally disintegrated? There are still chunks? What are we supposed to do with that information. Maybe some meteors are bigger than others and maybe they aren't. This doesn't connect to anything we know about the size, shape, or age of the stream. (C) The stream should not continue to exist for 5,000 years. Okay, but what we want to look at what has already happened. Also, the fact that the computer model covers a 5,000-year period does not tell us how much longer a 3,000-year-old meteor stream should last. (D) The stream has broadened as rapidly as the conventional theory predicted. This might seem to support the conventional theory and thereby pose a threat to the author's view. However, the distinction the author is making in the last paragraph between the two theories is not how fast the stream broadens, but whether it condenses or hollows out in the center. (E) The computer model does NOT provide an accurate representation of the development of the actual Geminid system. If that were the case, then it wouldn't be safe to use the model to determine the age of the system, even if its prediction about the hollow center seemed correct. If the stream took a much longer or shorter time to spread out than that predicted by the computer model, then it would not be safe to conclude that the stream is about 3,000 years old. Answer choice (E) as originally worded is a necessary assumption. I hope that helps!

KarishmaB · Answer

The point is not the length of the meteor shower but its thickness. The conventional theory says the distribution of particles would be increasingly dense toward the center of a meteor stream. So if Earth passes through a meteor stream, the density of particles will increase till Earth reaches the centre of the stream and then the density will start reducing again. Look at the diagram below: QUA-orbit.png The yellow part is the meteor stream. Earth (the blue dot) is passing through it on its orbit around the Sun (yellow dot). The density of particles will slowly increase till it reaches the centre and then gradually decrease again as per conventional theory

Carcass · Answer

I changed the tag to 700 because this was really tough and comes from OG 11th edition

Q. It can be inferred from the passage that which of the
following would most probably be observed during
the Earth's passage through a meteor stream if the
conventional theories mentioned in line 18 were
correct?

(A) Meteor activity would gradually increase to a
single, intense peak, and then gradually decline.

This is stated in the passage  "Conventional theories, however, predicted
that the distribution of particles would be
increasingly dense toward the center of a meteor
stream.

(B) Meteor activity would be steady throughout the
period of the meteor shower.

this contraddict A

(C) Meteor activity would rise to a peak at the
beginning and at the end of the meteor shower.

No is false

(D) Random bursts of very high meteor activity
would be interspersed with periods of very little
activity.

I didn't see anything about that

(E) In years in which the Earth passed through only
the outer areas of a meteor stream, meteor
activity would be absent.

I didn't see something about "absent"

The second one was even tough

The passage suggests that which of the following is a
prediction concerning meteor streams that can be
derived from both the conventional theories
mentioned in line 18 and the new computer-derived
theory?
(A) Dust particles in a meteor stream will usually be
distributed evenly throughout any cross section
of the stream.

Dust particles is not the poin of theories

(B) The orbits of most meteor streams should cross
the orbit of the Earth at some point and give rise
to a meteor shower.

neither the orbit

(C) Over time the distribution of dust in a meteor
stream will usually become denser at the outside
edges of the stream than at the center.

We know that is not true

D) Meteor showers caused by older meteor streams
should be, on average, longer in duration than those caused by very young meteor streams.

This is the line 8 "  Astronomers have
hypothesized that a meteor stream should broaden
with time as the dust particles' individual orbits are
perturbed by planetary gravitational fields.    The older is the meteor, more broaden is its stream, viceversa is a younger comet

(E) The individual dust particles in older meteor
streams should be, on average, smaller than those
that compose younger meteor streams.

Average is not the point of this inference question

jabhatta2 · Answer

Hi  VeritasPrepKarishma ,

Could you please discuss question 1 please

I chose A over B ...i thought this was about 2 theories (conventional theory mentioned in line 18 vs. what was seen in the computer model) hence chose A ...

Please let me know where did i go wrong with my logic

KarishmaB · Answer

Note that the passage has two paragraphs. The second paragraph does not compare the two theories at all. It just discusses the computer model and how it accurately modelled actual behaviour. 
Paragraph 1 discusses how the computer model simulates the two theories discussed.

Hence, the passage is all about the model.

Edith Wu · Answer

Hi,

I still don't understand Q4

Quote:
When the meteor streams are young, they’re more narrow; as they get older, they get broader.

Unquote.
According to the passage, my understanding is that the conventional theory argues that meteor streams get more and more narrow by time. Therefore, according to the conventional theory, meteor showers caused by older meteor streams should be shorter in duration than those caused by very young meteor streams.

Am I missing something?

Will2020 · Answer

Here is the OA for all the questions (OG 10th):

1.The primary focus of the passage is on which of the following?

This question asks you to identify the primary focus of the passage.

The best answer is B.  The author describes the new theoretical model in the first paragraph; in the final paragraph the author states that the data obtained from actual observations, which are discussed in the second and third paragraphs, is consistent with the new theoretical model.

Choice A is not correct; the computer model confirmed the astronomers’ hypothesis that meteor streams broaden with time, and although the model yielded an unexpected result, the passage does not contrast the predictions yielded by competing theories. Choice C and D are not correct because the passage makes no reference to further areas for research, and only a single phenomenon is described in the passage. And choice E is not correct because it reverses the order of events. The model yielded a prediction that was subsequently confirmed by observational data, the model was not constructed to explain the data.

2. According to the passage, which of the following is an accurate statement concerning meteor streams?

This question asks you to identify an accurate statement about meteor streams.  Choice C, the best answer , restates information about the composition of meteor streams from the first sentence of the passage.

Choice A is not correct. The passage discusses the influence of planetary gravitation on meteor streams but says nothing about its influence on the orbits of comets. According to the passage, it is planetary gravitation, not the gravitational fields of comets, that causes meteor streams to increase in size, so choice B is not correct. And choice D and E are not correct answers because the passage says nothing about the composition of comets or the role that meteor streams play in their further disintegration.

3. The author states that the research described in the first paragraph was undertaken in order to

This question asks what the author says about the purpose of the research described in the first paragraph.

The best answer is D.  According to the author, the purpose of the computer-modeling experiment was to test the hypothesis that meteor streams broaden with time.

Choice A is not correct; although the observational data described in the last paragraph allowed scientists to estimate the age of the Geminid stream, this data was analyzed to confirm a surprising prediction made by the computer model. This analysis was not part of the original experiment.

Choice B is also incorrect. Although the experiment yielded a surprising prediction about a particular feature of meteor streams, the purpose of the experiment was to determine whether meteor streams broaden with time, not to identify the various structural features of meteor streams.

Choice C is not correct because the experiment was undertaken to test a general hypothesis about meteor streams. It was not undertaken to explore the nature of any particular meteor stream, and 328 the passage never suggests that the actual meteor streams used in the computer model was “particularly interesting.”

Choice E is not correct. Although the computer model did confirm the astronomers’ hypothesis, the purpose of the experiment was not to show that such models are useful.

4. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?

This question asks you to make an inference about what would most probably be observed during the Earth’s passage through a meteor stream if the conventional theories mentioned in the passage were correct. According to line 18-20, the conventional theories predicted that the meteor stream would be most dense at the center. The computer model, one the other hand, predicted that a meteor stream would come to resemble a thick-walled, hollow pipe (lines 21-22). The passage states that, if the computer model were correct, two peak periods of meteor activity would be observed as the Earth passed through the walls of the “pipe” (lines 28-31). According to lines 36-38, observational data confirmed the prediction of the computer model. If, on the other hand, the conventional theories were correct, it can be inferred that a bifurcation of meteor activity would not be observed; instead, it can be inferred that scientists would expect to observe a single peak of meteor activity as the Earth passed through the dense center of the stream.

Choice A identifies this single peak of activity as the most likely observation if the conventional theories were correct.

Choice B and D are not correct because they describe meteor activity that is either steady or erratic, neither of which is consistent with the conventional theories. Choice C describes meteor activity more in line with the bifurcation predicted by the computer model, rather than the single peak of activity that the conventional theories would suggest. Choice E is incorrect because the passage says that meteor showers occur whenever the Earth passes through a meteor stream; it cannot be inferred that either theory would predict otherwise.

5. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?

This question asks for the reason given in the passage for a characteristic feature of meteor streams. According to lines 1-7, the dust particles in a meteor stream eventually surround a comet’s original orbit because of the different velocities at which they are ejected, as stated in choice  A, the best answer.

Choice B is directly contradicted by information in the passage (lines 8-10). The other answer choices re incorrect because the passage does not say that the dust particles become part of the meteor stream at different times, or that their velocity slows over time, or that their ejection velocity is slower than that of the comet.

6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?

This question asks you to identify a prediction that can be derived from both the conventional theories about meteor streams and the new computer-derived model. You must base your answer on information that is suggested by, but not expressly stated in, the passage.

According to lines 7-8 of the passage, the conventional theories hypothesized that meteor streams should broaden with time, and the computer simulation confirmed this hypothesis. The passage also suggests that the time it takes for the Earth to cross a meteor stream (and, by implication, the duration of the resulting meteor shower) is directly related to the breadth of the stream (lines 23-28). From these pieces of information, which are supported by both the conventional theories 329 and the new computer-derived theory, it can be inferred that on average the meteor showers caused by older (and therefore broader) meteor streams would be longer in duration than those caused by very young (and therefore narrower) meteor streams, as stated in  D, the best answer.

Choice A is incorrect because it contradicts the predictions of both the conventional theories (that the particles will be most dense at the center of the stream) and the computer model (that the stream will resemble a thick-walled, hollow pipe). Choice C is also incorrect because it is inconsistent with the conventional theories that suggested the distribution of dust in a meteor stream is denser at the center. And choices B and E are incorrect because the theories discussed in the passage do not suggest anything about the likelihood that the Earth’s orbit will cross that of any particular meteor stream, nor do they suggest anything about the size of the dust particles that compose meteor streams.

7. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

This question asks you to draw an inference from information in the last paragraph of the passage.

The best answer is C.  According to the passage, the Geminid meteor shower occurs yearly; because meteor showers occur whenever the Earth passes through a meteor stream, one can infer that the Earth crosses the Geminid stream once every year.

Choice A is incorrect because the passage provides no information from which to generalize about the age of meteor streams. Choice B, which is directly contradicted by lines 31-32, is also incorrect. Choice D is incorrect. In lines 25-28, the passage says that the Earth would take just over a day to cross the stream if the stream were 5,000 years old. However, in lines 38-42 the passage states that in fact an average of only 19 houses elapsed between the time that the Earth entered the stream until the time that it exited, leading researchers to conclude that the stream is only about 3,000 years old. Choice E is incorrect because the passage says only that planetary gravitational fields perturb the orbits of dust particles in a meteor stream; it does not say that the effect of the Earth’s gravitation is greater than that of other planets.

8. Which of the following is an assumption underlying the last sentence of the passage?

This question asks you to identify an assumption underlying the last sentence of the passage. In this sentence, the author of the passage draws a conclusion about the age of the Geminid stream.

This conclusion is based on two pieces of information. The first is the length of time the Earth would take to cross the computer-model Geminid stream if the stream were 5,000 years old (lines 24-28). The second is the actual elapsed time between the two peaks of meteor activity predicted by the computer model (lines 36-40). In concluding from this information that the Geminid stream is actually only 3,000 years old, the author is assuming the accuracy of the computer model, as stated in  E, the best answer.

Choice A is incorrect because the passage says that the time the Earth takes to cross the stream would vary from year to year (lines 32-34) and that 19 hours was the average time, not the exact time, observed from 1970 to 1979 (lines 36-40). Choices B and C are incorrect because the passage does not suggest anything about the current state of the comet associated with the Geminid stream or about the expected longevity of the stream. Choices D is incorrect because the computer model is said to confirm the broadening predicted by the conventional theories; the fact that the model projected the positions of the particles in the stream over a 5,000-year period does not suggest that researchers expected the stream to be older (and therefore broader) than it turned out to be.

ag28 · Answer

GMATNinja   VeritasKarishma   DmitryFarber

For Q7-
“actual yearly Geminid meteor shower“ - This doesn’t necessarily mean that Earth passes through the meteor shower as in option C.
However the passage does say that on average it takes a say to cross the meteor shower and the 19 hours can still lead to this average as in Option D

Please help

GMATNinja · Answer

Let's start with answer choice (C):

In the last paragraph, as you say, the author mentions the " yearly  Geminid meteor shower." In the 2nd paragraph, we also learn that "whenever the earth passes through a meteor stream, a meteor shower occurs."

Because the Geminid shower happens once per year (yearly), and because a meteor shower occurs every time the earth passes through a meteor stream, we can conclude that the earth passes through the Geminid meteor stream  once per year . So (C) is correct.

Let's consider (D):

The last paragraph tells us that the average time for the earth to pass through the meteor stream is  19 hours . This doesn't rule out the possibility that it usually takes more than a day, so (D)  could be  true. However, it's also  possible  that it usually takes less than a day. Since the question is asking which of the following  must be  true, (D) is incorrect.

I hope that helps!

Aviral1995 · Answer

VeritasKarishma   GMATNinja  please help me with Q-6

KarishmaB · Answer

The passage tells us:
 Astronomers have hypothesized that a meteor stream should broaden with time ... The researcher found, as expected, that the computer-model stream broadened with time.

So both agree that the meteor stream broadens with time. 
So when Earth passes through older meteor streams (which are broader), it will experience longer duration meteor showers (since Earth will take more time to cross a broader meteor stream)

Hence,

6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?

(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

(D) is correct.

suminha · Answer

Hi VeritasKarishma I'm confused

but the question was <<...derived from both the conventional theories mentioned in line 18...>>.. How come you cite <> since it's not conventional theories's assumption...? Please help me

Thank you !

KarishmaB · Answer

Astronomers have hypothesized that a meteor stream should broaden with time ...

This is the conventional theory. It is what astronomers have hypothesised.

The researcher found, as expected, that the computer-model stream broadened with time.

This is what they found on the computer model so it is the computer derived theory.

Both agree on this point.

suminha · Answer

Thanks for your reply  VeritasKarishma  !
I see the structure that you mentioned, “Astronomers have hypothesis that meteor stream should broaden with time” is Main idea here and Conventional theory is supporting idea so the conventional theory = Astronomer’s hypothesis.

However, what drives me crazy is that  each “broaden with time” and “dense toward the center” demonstrates opposite direction.  
 I don’t understand how something can broaden with time, becoming denser towards the center.  That’s why I thought astronomers’ assumption and conventional theory’s assertion are different.... Moreover, there is “however” after the conventional theory, putting more weight on the idea that they are going opposite direction.... ?

Posted from my mobile device

KarishmaB · Answer

'Broaden with time' and 'dense toward the centre' are not conflicting parameters. 19461373_105.png Look at this stream. It is narrow at places (top and bottom of picture) and broader at others (centre of picture). The entire stream broadens with time. Also, the stream could have a lot of particles in the centre and relatively fewer at the edges (not apparent in the picture).

egmat · Answer

Hey folks,

I had the pleasure of going through this passage recently. Here are some notes from my analysis - based on my understanding. Hoping this is useful for students.

Passage Analysis 
- Meteor stream: made of dust particles ejected from a comet, at various velocities
- Some particles go faster, they move ahead of the comet, some particles go slower, they fall behind. Net effect: a shroud of dust surrounding the entire comet, forming a stream
-  Astronomer's Hypothesis :  meteor stream should broaden with time , because the dust particles’ individual orbits are impacted by planetary gravitation fields. This is the existing hypothesis  (so, the conventional idea about this thing) 
- Recent Computer simulation: done to test the above hypothesis (does a meteor stream broaden with time?)
-  Simulation Result:   Yes, meteor stream does broaden with time.  
-  Conventional Theory:  Distribution of dust particles in a meteor stream - light at the edges, dense at the center  (like the bell shaped curve in statistics -  visualize  )
-  Actual Observation from the Model:  Dense at the edges, light at the center (like a thick walled, hollow pipe)
- Whenever the earth passes through a meteor stream, a meteor shower occurs 
- As per Model: If the stream were 5000 years old, earth would take just over a day (24 hrs) to cross the meteor stream, moving at 15L miles/day around the orbit of the meteor stream.
- As per Model: Two brief separate periods of peak meteor activity.  This is like the earth cutting through the cross-section of a thick hollow pipe,   - visualize  . Dense/heavy at the entry and exit (peak meteor activity), light at the center. In other words: Model suggests thick hollow pipe theory, not conventional theory.
- Time interval between the 2 bursts varies (because the earth does not have to move through exact center - may/may not). Varies from one year to the next.  Inference:   This means earth going through a meteor stream is a yearly event. 
- Actual Real life data supports the model i.e. model is accurate
- Thick walled hollow pipe is what is actually seen - 2 bursts of activity, 19 hours apart (not 24 hours). Dense at the extremes, light at the center.
- When the model used 5000 years as age at input -> greater than 24 hours (time); What we saw: 3000 years (actual) -> 19 hours. Suggests that  Older the meteor, longer the duration of the meteor shower   (visualize this: pipe with a larger diameter - takes longer for the earth to go through the cross section. Older meteor, longer duration).

Hope this helps create a better understanding of this passage.

Cheers!
Harsha

danymasri98 · Answer

Could anyone explain why D is wrong and E is correct?
I can't seem to understand why we have to assume that the computer model was correct

GMATNinja · Answer

Question 8 
 
Question 8 asks us for "an assumption underlying the last sentence of the passage."

That last sentence reads: "The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old."

The author provides the following evidence to reach this conclusion:

Meteor streams spread out over time.
 
 A computer model predicted that a meteor stream would create a "hollow pipe" shape.
 
 It also predicted that, if the Geminid stream were 5000 years old, the earth would take "just over a day" to pass through the pipe. So, you'd have a bunch of meteor activity one day, and then a bit over a day later you'd have a bunch more meteor activity.
 
 In actual data, there was actually just  under  a day between peak meteor activity.

So, the actual data from 1970-1979 matches a  narrower  pipe than the one in the 5000 year old model. Because meteor streams get  wider  over time, this shows that the Geminid stream is younger than the model -- it's 3000 years old, not 5000 years old.

Which answer choice do we NEED to assume to reach this conclusion?

Here's (D):

"Conventional theories" predicted a pattern that is totally different than the "hollow pipe" pattern. According to these theories, you shouldn't have a first burst and then a second burst at all -- instead, you'd have only  one  peak meteor time.

But the data referenced in the last sentence DOES match the "hollow pipe" pattern. The author has pretty much thrown out the "conventional theories" altogether, and instead provides support for the "hollow pipe" theory.

Since the argument in the last sentence has nothing to do with the conventional theories, the author doesn't need to assume the information in (D).

Here's (E):

How does the author reach the conclusion that the Geminid meteor stream is 3000 years old? It all relies on the computer model. That model says that if it were 5000 years old, the pipe would be wide enough to cause over a day between bursts of meteor activity.  Relative to this prediction , the actual data shows that the pipe is skinner, which means that the stream must be a bit younger than 5000 years.

Because the conclusion entirely depends on the computer's prediction, we NEED to assume that this prediction is accurate. Without that assumption, there is no support at all for the claim that the stream is 3000 years old.

The last sentence relies on the assumption in (E), so (E) is the correct answer to question 8.

I hope that helps!

KarishmaB · Answer

Question 1.

Break down the passage. Main point of the 3 paragraphs:

Para 1 - Tells us that the computer model predicted a thick-walled, hollow pipe.
Para 2 - Discusses what should be observed if this is true.
Para 3 - Tells us that this is true! (with actual values observed)

1.The primary focus of the passage is on which of the following?

(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
 
Conventional theory is also mentioned but no predictions are made about it.

(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
 
Correct. It describes the computer model and notes that the model explains the actual observations.

(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
 
No discussion on 'further areas for research'. Eliminate.

(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
 
Only one natural phenomenon discussed. Doesn't tell us how measurements are taken.

(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data
 
This switches the order of the events. The computer model predicted a hollow pipe and the observations confirmed it. This option says that we first observed the data and then concluded that it must be a hollow pipe. That is not correct. The computer model predicted it and afterwards we observed the data and figured that it does support the hollow pipe hypothesis.

Answer (B)

A meteor stream is composed of dust particles that have been ejected

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

A meteor stream is composed of dust particles that have been ejected

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