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GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn

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GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 12 Aug 2014, 04:46
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Passage-12 GMATPrep RCs-Collection(Main article)
In the 1980's, astronomer Bohdan Paczynski proposed a way of determining whether the enormous dark halo constituting the outermost part of the Milky Way galaxy is composed of MACHO's (massive compact halo objects), which are astronomical objects too dim to be visible. Paczynski reasoned that if MACHO's make up this halo, a MACHO would occasionally drift in front of a star in the Large Magellanic Cloud, a bright galaxy near the Milky Way. The gravity of a MACHO that had so drifted, astronomers agree, would cause the star's light rays, which would otherwise diverge, to bend together so that, as observed from Earth, the star would temporarily appear to brighten, a process known as microlensing. Because many individual stars are of intrinsically variable brightness, some astronomers have contended that the brightening of intrinsically variable stars can be mistaken for microlensing. However, whereas the different colors of light emitted by an intrinsically variable star are affected differently when the star brightens, all of a star's colors are equally affected by microlensing. Thus, if a MACHO magnifies a star's red light tenfold, it will do the same to the star's blue light and yellow light. Moreover, it is highly unlikely that a star in the Large Magellanic Cloud will undergo microlensing more than once, because the chance that a second MACHO would pass in front of exactly the same star is minuscule.
1. The passage is primarily concerned with
A. outlining reasons why a particular theory is no longer credited by some astronomers
B. presenting data collected by a researcher in response to some astronomers' criticism of a particular line of reasoning
C. explaining why a researcher proposed a particular theory and illustrating how influential that theory has been
D. showing how a researcher's theory has been used to settle a dispute between the researcher and some astronomers
E. describing a line of reasoning put forth by a researcher and addressing a contention concerning that line of reasoning
[Reveal] Spoiler:
E


2. According to the passage, Paczynski's theory presumes that if MACHO's constituted the Milky Way's dark halo, occasionally a MACHO would
A. drift so as to lie in a direct line between two stars in the outer Milky Way
B. affect the light rays of a star in the Large Magellanic Cloud with the result that the star would seem for a time to brighten
C. become obscured as a result of the microlensing of a star in the Large Magellanic Cloud
D. temporarily increase the apparent brightness of a star in the Large Magellanic Cloud by increasing the gravity of the star
E. magnify each color in the spectrum of a star in the Large Magellanic Cloud by a different amount
[Reveal] Spoiler:
B


3. It can be inferred from the passage that which of the following would constitute the strongest evidence of the microlensing of a star in the Large Magellanic Cloud?
A. The brightness of such a star is observed to vary at irregular intervals.
B. The brightening of such a star is observed to be of shorter duration than the brightening of neighboring stars.
C. The red light of such a star is observed to be brighter than its yellow light and its blue light.
D. The red light, yellow light, and blue light of such a star are observed to be magnified temporarily by the same factor.
E. The red light of such a star is observed to have increased tenfold.
[Reveal] Spoiler:
D


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Last edited by PiyushK on 16 Aug 2014, 02:01, edited 3 times in total.
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 12 Aug 2014, 08:41

Time taken 7:35 min. What shld be the expected timing for this Q?
1. The passage is primarily concerned with
E. describing a line of reasoning put forth by a researcher and addressing a contention concerning that line of reasoning
" astronomer Bohdan Paczynski proposed a way of determining whether the enormous dark halo constituting the outermost part of the Milky Way galaxy is composed of MACHO's
blah blah
Because many individual stars are of intrinsically variable brightness, some astronomers have contended that
blah
blah
However, whereas the different colors of light emitted by an intrinsically variable
"

2. According to the passage, Paczynski's theory presumes that if MACHO's constituted the Milky Way's dark halo, occasionally a MACHO would
B. affect the light rays of a star in the Large Magellanic Cloud with the result that the star would seem for a time to brighten
>>Got this by elimination. Also the language seems to match the para. What I didn't understand is the meaning of "the star would seem for a time to brighten".

3. It can be inferred from the passage that which of the following would constitute the strongest evidence of the microlensing of a star in the Large Magellanic Cloud?
D. The red light, yellow light, and blue light of such a star are observed to be magnified temporarily by the same factor.
>>if a MACHO magnifies a star's red light tenfold, it will do the same to the star's blue light and yellow light.
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Last edited by PiyushK on 13 Aug 2014, 20:29, edited 1 time in total.
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 12 Aug 2014, 09:53
JarvisR wrote:
Time taken 7:35 min. What shld be the expected timing for this Q?


I believe between 5-7min is sufficient for this short RC.
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 12 Aug 2014, 19:39
for many short passages in og, gmatprep, the first question about the main idea is hard while the second or third question about a detail in the passage is easy. this passage is an example of this point.

for 2 and 3, the answer is B and D clearly.

for the first, which I feel hard, the answer is C.
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 14 Aug 2014, 23:56
I took 7min++ approx.
E B D (all correct)

OAs are also updated.

Passage was overall easy but it has so many modifiers that affected my thread often.
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 15 Aug 2014, 02:37
PiyushK wrote:
I took 7min++ approx.
E B D (all correct)

OAs are also updated.

Passage was overall easy but it has so many modifiers that affected my thread often.


hi, could you please explain me why B and not D, for Q2

thanks!
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 15 Aug 2014, 22:21
Hi adymehta29,
Below is my reasoning to cancel D.
D)temporarily increase the apparent brightness of a star in the Large Magellanic Cloud by increasing the gravity of the star.
"The gravity of a MACHO that had so drifted, astronomers agree, would cause the star's light rays, which would otherwise diverge, to bend together so that, as observed from Earth, the star would temporarily appear to brighten, a process known as microlensing."

As per the argument, MACHO doesn't increase the gravity to achieve mentioned effect. It's the "drifted gravity " that does it.

Hope this answers your query.
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GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 25 Aug 2014, 11:57
My answers

1.E
2.B
3.D

Time taken - 5mins 45 secs - spent wat too much time with Q1
I am struggling with Primary purpose questions. Would appreciate if someone can share his method. Thnx
Great post once again. :)
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Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn [#permalink] New post 01 Oct 2014, 21:43
got the 1st Q wrong.. can anybody please explain this Qstn and similar types
Re: GMATPREP ChallengeQ -In the 1980's, astronomer Bohdan Paczyn   [#permalink] 01 Oct 2014, 21:43
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