Comets do not give off their own light but reflect light : GMAT Critical Reasoning (CR)
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# Comets do not give off their own light but reflect light

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Director
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Comets do not give off their own light but reflect light [#permalink]

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22 Jan 2007, 10:24
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Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a cometâ€™s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halleyâ€™s comet is composed reflects 60 times less light per unit of mass than had been previously thought.
The statements above, if true, give the most support to which one of the following?
(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halleyâ€™s comet is composed.
(B) Previous estimates of the mass of Halleyâ€™s comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halleyâ€™s comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.
(E) Scientists need more information before they can make a good estimate of the mass of Halleyâ€™s comet.

I am caught b/w B or C...
If you have any questions
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22 Jan 2007, 12:24
I would say C
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22 Jan 2007, 19:06
vineetgupta wrote:
Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a cometâ€™s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halleyâ€™s comet is composed reflects 60 times less light per unit of mass than had been previously thought.
The statements above, if true, give the most support to which one of the following?
(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halleyâ€™s comet is composed.
(B) Previous estimates of the mass of Halleyâ€™s comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halleyâ€™s comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.
(E) Scientists need more information before they can make a good estimate of the mass of Halleyâ€™s comet.

I am caught b/w B or C...

C.
Greater Mass = More Light
Scientists determined Halley has 60 times LESS light than they thought, so it has LESS mass.
C is the best conclusion derived from the stem because it is pulled directly from the statements and does not go at all beyond what is said.

B actually says the opposite of the stem.
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22 Jan 2007, 20:22
C... too...

in B, you have no idea how good/bad the previous estimate was to be affected by this change..
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22 Jan 2007, 22:28
choice C

choice B goes the other way.
Previous estimates of the mass of Halleyâ€™s comet which were base on its brightness were too low.
if previous estimates were low,implies the mass should have been more than thought.with more mass, the brightness hosuld be more and not less as found out.
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23 Jan 2007, 05:26
What is OA?
B looks correct to me
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23 Jan 2007, 06:34
P - Comets reflect light from other sources.
P - Brightness = Mass of comets
P - Greater Mass Greater the light reflection
P - Halley's comet reflects 60 times less/per unit mass

E - Out of Scope
D - Argument talks about mass of the comet not reflective properties
B - Out of Scope
A - Opposite of what the argument states
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26 Jan 2007, 10:34
I also chose C...but the OA is given as B.

How is B out of scope?...
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26 Jan 2007, 11:11
I read the problem; and before reading the responses - I adamentaly chose B. Then read the responses and was surprised to see the answer was C, until I read last post and the OA did say the answer was in B. I am glad I was right and not out of my mind.

I will attempt to try and explain why the answer is B as clearly as possible.

The assertion made in the problem, by scientists, is that their is a direct relationship between a comets mass and the light which it reflects. The problem goes on to say that with the case of Haley's comet the material of which it is composed was found to reflect 60 times less light per unit of mass (than originally presumed).

Ok. So this means, simply, the light Haley's comet reflected was not an accurate depiction of how its mass. The problem states, that more light = more mass. If it reflected less light (because of its material - that was unbeknown to scientist) this means the original estimate ofs its mass was negatively proportianate. Basically "previous estimates of the mass from Haley's comet which were based on its brightness were too low". The answer is clearly B.

So why not C? C has nothing to do with what scientists estimated. Scientists estimated the comets mass, based off its quanitfiable brightness. The total amount of light it reflected was not more/or less than what scientists had previously thought; it was what it was. I hope I make sense.

I have not taken the GMAT, I have only taked the Gmat prep test 1, and scored a 690. (45 Q, and 40 V).
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