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505-555 Level|   Long Passage|   Science|         
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 30 Dec 2019, 10:28
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carcass Can you help with the following question?

The method used by Wadati to determine the depths of earthquakes is most like which of the following?
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I have provided a detailed solution, check it out
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 30 Dec 2019, 10:36
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Businessconquerer Can you share the link pls? Thanks.
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 30 Dec 2019, 10:47
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Businessconquerer Can you share the link pls? Thanks.
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My bad GMAT Ninja answered my doubts here, truly sorry. I have actually answered almost all tricky official questions so.. got confused
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 08 Jan 2020, 20:07
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VeritasKarishma

I went through your explanation ( Q 6) on why "stress"must be required in "any" earth quack.

But, I am still not convinced.

For shallow earthquakes : Stress builds up -> fracture forms at a depth -> crust cracks
So, both Stress and fracture are required.

BUT
For deep earthquakes, it says - how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture?
Here, "stress' is expected for fracture.
Now, at last - The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
But, did the (expected) stressed result the fracture?
Not mentioned. All we know that fracture happened for deep earthquakes.

How can we assume that the required stress was built-up and fracture did not happen by any other reason( e.g collisions of the plates etc)?
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 08 Jan 2020, 23:07
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VeritasKarishma

I went through your explanation ( Q 6) on why "stress"must be required in "any" earth quack.

But, I am still not convinced.

For shallow earthquakes : Stress builds up -> fracture forms at a depth -> crust cracks
So, both Stress and fracture are required.

BUT
For deep earthquakes, it says - how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture?
Here, "stress' is expected for fracture.
Now, at last - The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
But, did the (expected) stressed result the fracture?
Not mentioned. All we know that fracture happened for deep earthquakes.

How can we assume that the required stress was built-up and fracture did not happen by any other reason( e.g collisions of the plates etc)?
Show more


The problem with deep earthquakes was how would fracture happen? Stress build up is the starting point. For an earthquake, a fracture is needed too. The passage explains us that it seems simple enough for shallow quakes but how does it happen in deep ones because there is nothing to fracture even under immense stress. At the end the passage gives us what will fracture. It is obvious that stress will cause the fracture.
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 15 Jan 2020, 20:26
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mimishyu
5.The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.---correct
(E) The epicenter is in the crust, whereas the focus is in the mantle.


I’m really confused about option(E)
About option(E), maybe we can infer
from the first sentence of para3

For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest.

Also from first & second sentence of para1

In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle,
-we can infer that ‘’The epicenter is in the crust’’

However, in para1, we know that focus(The focus of an earthquake is the point where the rocks start to fracture. It is the origin of the earthquake.)can be occur both in crust or mantle, if it occur in crust, it’s not far away from epicenter, maybe just a very little distance below epicenter????
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Sorry for the late reply, mimishyu -- I just noticed your question behind a bunch of other posts.

You're right to point out that the focus (defined as the earthquake's "rupture point") can be in the crust OR in the mantle. This, however, is a reason to eliminate (E), not keep it.

Choice (E) says:

Quote:
(E) The epicenter is in the crust, whereas the focus is in the mantle.
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This description implies that the epicenter is ONLY in the crust, whereas the focus is ONLY in the mantle. It doesn't mention or imply any possibility for the focus to be in the crust as well.

This does NOT reflect the relationship between epicenter and focus that's written in the passage, and that's why we eliminate (E).

I hope that helps!
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VeritasKarishma carcass AjiteshArun
Can you please explain the Q8 I was confused between A and B
I choose OA as B because Wadii used P and S waves and the researcher before that didn't.
Though A is true as mentioned in the first line of the paragraph 2
The passage says that other people accepted the existence of deep events "only since 1927". It doesn't say (for sure) that they rejected the use of P-S intervals to determine the depths of earthquakes. In the sentence that you are probably looking at:

Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves.

We know only that they used method X and that Wadati used method Y. This is not enough to say that they rejected method Y. Maybe they just didn't know about it. Maybe Wadati was the first to come up with the idea to apply P-S intervals to this problem. Maybe. The point is that because we don't know any of this for sure, and because we know that what option A says is true as per the passage, we should pick option A over B.
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Dear sir, could you please explain the correct answer for the question.? Thank you in advance.
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Quote:
6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.
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Query on II

WHy II is not correct?

Quote:
The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
Show more
If the rock does not descend how the fracture can happen ultimately.

SO if III is true , i think II must also be true.
Otherwise without descend why the rock would fracture as it is more ductile before descend into mantle.

please clarify GMATNinja VeritasKarishma AjiteshArun carcass sayantanc2k saswata4s Skywalker18
please suggest
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 14 Sep 2020, 22:47
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Quote:
6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.

Query on II

WHy II is not correct?

Quote:
The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
If the rock does not descend how the fracture can happen ultimately.

SO if III is true , i think II must also be true.
Otherwise without descend why the rock would fracture as it is more ductile before descend into mantle.

please clarify GMATNinja VeritasKarishma AjiteshArun carcass sayantanc2k saswata4s Skywalker18
please suggest
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Hi imSKR,

The question is: "The passage suggests that which of the following must take place in order for any earthquake to occur?" That is, this question is not limited to deep quakes. That's the reason statement II is not correct (it doesn't apply to quakes other than deep quakes, so it can't be the answer to a question about "any earthquake").
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4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance

Dear Experts and Colleagues, can anyone please help me to understand the answer to Question nr 4 of the above RC.
I am not able to co-relate between the passage and this question.
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4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance

Dear Experts and Colleagues, can anyone please help me to understand the answer to Question nr 4 of the above RC.
I am not able to co-relate between the passage and this question.
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Hi axon321,

Question 4 is an analogous question, where you need to compare the method Wadati used to determine the depths of earthquakes :

Quote:
Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.
Show more

Wadati measures the time difference in the arrival of P waves and the arrival of S waves, implying that S arrives a little late than the P waves and that difference between their arrival times increases with their distance from the earthquake focus, or rupture point. Thus, the more the interval between the two waves the farther they are from the rupture point.
So we need to look for an option that also includes a similar relation between the distance and the difference in the interval of two similar waves/entities.

The best co-relation is suggested by Option C. You might want to give it a try now. Let me know if you still have doubts.


Thanks.
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But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
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Respected GMATNinja Sir,

I got only this question wrong and I am unable to wrap my head around options A and C, even after going through your above-mentioned explanation.

What I understood from the passage:
Both the time intervals of P-S and difference in intensity say that we have 2 kinds of earthquakes - 1. Shallow ones, in which focus is just beneath epicenter and 2. Deep ones, in which focus is hundreds of kilometers down.

Now,
Quote:
3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(C) The earthquake focus was distant.
Show more

I am not able to understand on what basis should I eliminate option A because, in the passage, 2nd point mentions that such events are deep ones in which focus is way beneath the epicenter. I am finding options A and C equally correct. :(
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Question 3


sssanskaar
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Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!

Respected GMATNinja Sir,

I got only this question wrong and I am unable to wrap my head around options A and C, even after going through your above-mentioned explanation.

What I understood from the passage:
Both the time intervals of P-S and difference in intensity say that we have 2 kinds of earthquakes - 1. Shallow ones, in which focus is just beneath epicenter and 2. Deep ones, in which focus is hundreds of kilometers down.

Now,
Quote:
3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(C) The earthquake focus was distant.

I am not able to understand on what basis should I eliminate option A because, in the passage, 2nd point mentions that such events are deep ones in which focus is way beneath the epicenter. I am finding options A and C equally correct. :(
Show more
Question 3 is also discussed in this post, but read below for further explanation.

Imagine the following scenarios:

    1) There is a shallow earthquake in Paris, and you measure the time between P and S waves while you're standing in Paris.

      In this scenario, there would be a very SHORT time in between P and S waves, because you're close to the focus of the earthquake.

    2) There is a deep earthquake in Paris, and you measure the time between P and S waves while you're standing in Paris.

      Now, there would be a LONG time between P and S waves, because the focus of the earthquake is deep under the earth.

    3) There is a shallow earthquake in Paris, and you measure the time between P and S waves while you're standing in hundreds of miles away in Berlin.

      There would be a LONG time between P and S waves, because the focus of the earthquake is far away.

    4) There is a deep earthquake in Paris, and you measure the time between P and S waves while you're standing in hundreds of miles away in Berlin.

      There would still be a LONG time between P and S waves, because the focus of the earthquake is far away.

Question 3 asks us what we can infer if there is a LONG time in between P and S waves. You can see from above that there would be a long time in between the waves in scenarios 2), 3), and 4).

Scenarios 2) and 4) involve deep earthquakes, but scenario 3) involves a shallow earthquake. So, we can't infer that a long time between P and S waves means that the earthquake is deep -- all we can say is that the focus of the earthquake is far away.

(A) is out for question 3, and (C) is the correct answer.

I hope that helps!
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Dear GMATNinja

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

I can pick the right choice thank to this information "Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus". However, I also confused for choice A until I read your below explanation. Thank you very much.

But I have an unclear point: Where does the passage mention or imply that the method of Wadati used to measure intervals is taking these mesurements at different locations? such as your example at earlier explanation: "Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.
What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer."

In deed, if the passage has such implication, I would not have confused when elimated A



GMATNinja
Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
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Dear GMATNinja

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

I can pick the right choice thank to this information "Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus". However, I also confused for choice A until I read your below explanation. Thank you very much.

But I have an unclear point: Where does the passage mention or imply that the method of Wadati used to measure intervals is taking these mesurements at different locations? such as your example at earlier explanation: "Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.
What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer."

In deed, if the passage has such implication, I would not have confused when elimated A



GMATNinja
Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
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The passage does not imply that Wadati’s method takes measurements at different locations for the same earthquake. In fact, it indicates the opposite:

    Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

The question becomes where the P and S waves were measured for this particular earthquake. They were measured at a single location, but we don’t know how far away from the epicenter that location was.

As we said in our previous post, if the location of the measurements was near the earthquake, the earthquake was likely deep. But if that location was far from the earthquake, the earthquake may not have been deep. For that reason, we can eliminate (A).

I hope that helps!
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 24 Feb 2021, 22:55
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Thank you sir GMATNinja

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TrungTiger
Dear GMATNinja

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

I can pick the right choice thank to this information "Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus". However, I also confused for choice A until I read your below explanation. Thank you very much.

But I have an unclear point: Where does the passage mention or imply that the method of Wadati used to measure intervals is taking these mesurements at different locations? such as your example at earlier explanation: "Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.
What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer."

In deed, if the passage has such implication, I would not have confused when elimated A



The passage does not imply that Wadati’s method takes measurements at different locations for the same earthquake. In fact, it indicates the opposite:

    Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

The question becomes where the P and S waves were measured for this particular earthquake. They were measured at a single location, but we don’t know how far away from the epicenter that location was.

As we said in our previous post, if the location of the measurements was near the earthquake, the earthquake was likely deep. But if that location was far from the earthquake, the earthquake may not have been deep. For that reason, we can eliminate (A).

I hope that helps!
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 08 Dec 2021, 03:16
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Can anyone explain the Application question - Q7?
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 09 Dec 2021, 00:47
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Can anyone explain the Application question - Q7?
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Explanation to question #7 is posted here in the link below

https://gmatclub.com/forum/in-most-eart ... l#p1797162

Happy prep.
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In most earthquakes the Earth’s crust cracks like porcelain. Stress bu 21 Dec 2021, 10:39
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Could you please expain 3, 5. and 9th question.
My answers:
3 A
5 C
9 C
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Could you please expain 3, 5. and 9th question.
My answers:
3 A
5 C
9 C
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Hello shrya

Welcome to GMAT Club!

This passage is extensively discussed. You can find explanations in the following links.

Question #3

https://gmatclub.com/forum/in-most-eart ... l#p2083094

https://gmatclub.com/forum/in-most-eart ... l#p2325622

Question #5

https://gmatclub.com/forum/in-most-eart ... l#p2329739

Question #9

https://gmatclub.com/forum/in-most-eart ... l#p1976261

https://gmatclub.com/forum/in-most-eart ... l#p1976580

Good luck!
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