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# Scientist: Our antenna has located a new signal. This signal

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Scientist: Our antenna has located a new signal. This signal [#permalink]

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23 Nov 2012, 07:50
00:00

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(N/A)

Question Stats:

71% (02:05) correct 29% (01:41) wrong based on 66 sessions

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Scientist: Our antenna has located a new signal. This signal may be from space, or it might be the result of
interference from equipment on Earth. In order to determine which it is, we plan to test this signal by slightly
changing the orientation of our antenna. Much as a searchlight beam falls off in intensity near its edges, so too does
the sensitivity of an antenna decrease when a transmitting target is not exactly centered. If the signal intensity
increases or decreases, then we have evidence that the signal is from space.

The scientist’s plan assumes that

A. the antenna is currently oriented to the center of the transmitting target
B. the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is
C. adjusting the antenna orientation is the test most likely to eliminate the possibility of Earth-based interference
D. Earth-based interference is likely to appear as if it were being transmitted from several specific locations at once
E. signal transmissions from space are less intense than Earth-based interference

OA
[Reveal] Spoiler:
later

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Re: Our antenna has located a new signal [#permalink]

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23 Nov 2012, 09:00
I choose B after 1'54''
A. the antenna is currently oriented to the center of the transmitting target
not really know
B. the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is
C. adjusting the antenna orientation is the test most likely to eliminate the possibility of Earth-based interference
not really know. The answer also contains "most", the extreme word, which should be avoided.
D. Earth-based interference is likely to appear as if it were being transmitted from several specific locations at once
not relevant
E. signal transmissions from space are less intense than Earth-based interference
not relevant
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Re: Our antenna has located a new signal [#permalink]

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23 Nov 2012, 12:21
gmatbull wrote:
Scientist: Our antenna has located a new signal. This signal may be from space, or it might be the result of
interference from equipment on Earth. In order to determine which it is, we plan to test this signal by slightly
changing the orientation of our antenna. Much as a searchlight beam falls off in intensity near its edges, so too does
the sensitivity of an antenna decrease when a transmitting target is not exactly centered. If the signal intensity
increases or decreases, then we have evidence that the signal is from space.

OA
[Reveal] Spoiler:
later

The scientist’s plan assumes that

A. the antenna is currently oriented to the center of the transmitting target - this acts opposite to the argument. The premise states "sensitivity" of an antenna decreases when a target is not exactly centered. This option does not even tie to the conclusion. Eliminate.
B. the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is
slightly adjusted - Yes - If the signal intensity increases or decreases we have that evidence that the signal is from space. Therfore, intensity of signals produced on Earth should remain constant.
C. adjusting the antenna orientation is the test most likely to eliminate the possibility of Earth-based interference - nope - Doesn't tie to the conclusion.
D. Earth-based interference is likely to appear as if it were being transmitted from several specific locations at once - Out of scope.
E. signal transmissions from space are less intense than Earth-based interference - how can you say this ? Eliminate.

Arrive at B .
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Re: Our antenna has located a new signal [#permalink]

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23 Nov 2012, 14:08
The stem says the interference might be from equipment on Earth, but option B says
"intensity of signals produced by interference on Earth remains "

What effect is the statement on the validity of the argument?
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Re: Our antenna has located a new signal [#permalink]

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23 Nov 2012, 23:51
gmatbull wrote:
The stem says the interference might be from equipment on Earth, but option B says
"intensity of signals produced by interference on Earth remains "

What effect is the statement on the validity of the argument?

The conclusion of the statement : If the signal intensity increases or decreases, then we have evidence that the signal is from space.

We need to tie the option as closely to the conclusion as possible.

So, if the conclusion needs to hold true :
We need to assume :
the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is slightly adjusted.

If the intensity is increases or decreases from space , we need to assume the intensity on Earth is constant.

Even if you try negating this option, you should be able to come to B.

I hope that helps !
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Re: Our antenna has located a new signal [#permalink]

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25 Nov 2012, 20:22
gmatbull wrote:
Scientist: Our antenna has located a new signal. This signal may be from space, or it might be the result of
interference from equipment on Earth. In order to determine which it is, we plan to test this signal by slightly
changing the orientation of our antenna. Much as a searchlight beam falls off in intensity near its edges, so too does
the sensitivity of an antenna decrease when a transmitting target is not exactly centered. If the signal intensity
increases or decreases, then we have evidence that the signal is from space.

The scientist’s plan assumes that

A. the antenna is currently oriented to the center of the transmitting target
B. the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is
C. adjusting the antenna orientation is the test most likely to eliminate the possibility of Earth-based interference
D. Earth-based interference is likely to appear as if it were being transmitted from several specific locations at once
E. signal transmissions from space are less intense than Earth-based interference

OA
[Reveal] Spoiler:
later

Excellent Question
Conclusion: If the orientation of the antenna is changed and the signal increases or decreases than it means that the signal is not from the interfernce of the earth.

I eliminated all choices except B and C, B wins in the negation test.

Lets check B the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is
slightly adjusted when negated it becomes "the intensity of signals produced by interference on Earth does not remains constant when an antenna’s orientation is slightly adjusted "
That means when the signal increases or decreases that is to say changes than the signal is from earth's interfernce.Hence the conclusion is destroyed.

C. adjusting the antenna orientation is the test most likely to eliminate the possibility of Earth-based interference>>>The argument is not concerned with the type or various tests required to check interference. the argument is specific about the type of test described in the argument.
Moreover when the option is negated it means that the test described in the argument is not the only test, there are other type of tests to eliminate the possibility, the choice does not weaken anyway the result of the test mentioned in the argument.
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Re: Our antenna has located a new signal [#permalink]

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26 Nov 2012, 05:11
i feel that the answer is A because if the scientist did not assume A then his conclusion cannot be drawn.
i deliberated a lot between A and B but finally chose A.
while making the conclusion i feel the scientist is worried less about the interference produced by objects on the earth.
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Re: Our antenna has located a new signal [#permalink]

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26 Nov 2012, 08:32
Hi Siriam,

The answer is almost certainly B.

A is no good because that conclusion about the 'centering' does not actually address something about either the signal being from space or earth. If it is currently centered it could be on either an object in space or on earth.

Hope that helps.

Cheers,

James
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Re: Our antenna has located a new signal [#permalink]

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26 Nov 2012, 15:09
plumber250 wrote:
Hi Siriam,

The answer is almost certainly B.

A is no good because that conclusion about the 'centering' does not actually address something about either the signal being from space or earth. If it is currently centered it could be on either an object in space or on earth.

Hope that helps.

Cheers,

James

hi plumber250,

i agree with your thought but look at the argument in this way.
to decide signal source, the author decides to use a certain method to eliminate the wrong one.
author has thought of that method because he has assumed that whatever transmission the antenna is receiving is from the center of the signal source.
so i thought that this was the fundamental assumption of the author while writing this piece of argument.
can you please explain to me where i have gone wrong.
thanks!!
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Re: Our antenna has located a new signal [#permalink]

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26 Nov 2012, 15:48
Hi Siriam,

In my opinion the hitting of the centre is neither assumed or necessary. We know nothing about whether hitting the centre of the target is necessary for this to work, so it's irrelevant to the argument presented.

I may be wrong. Time for the OA please...

Thanks

James
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Re: Our antenna has located a new signal [#permalink]

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26 Nov 2012, 16:00
hi plumber,

the OA is definitely B because if you negate B it weakens the argument.
negation of B- the intensity of signals produced by interference on earth does not remain constant when antenna's orientation is slightly adjusted.

this weakens authors conclusion that signal is from outer space.

i agree that B is indeed better than A.
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Re: Scientist: Our antenna has located a new signal. This signal [#permalink]

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03 Dec 2012, 11:24
The answer should be B because if negate the following option "the intensity of signals produced by interference on Earth remains constant when an antenna’s orientation is slightly adjusted" then it conclusion untrue.
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Re: Scientist: Our antenna has located a new signal. This signal [#permalink]

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04 Dec 2012, 01:41
Of course, we have an overwhelming majority leaning towards
[Reveal] Spoiler:
B
, and it's the OA.
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Re: Scientist: Our antenna has located a new signal. This signal   [#permalink] 04 Dec 2012, 01:41
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