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800GMAT · Tue May 29, 2007 1:18 am

Brown dwarfs-dim red stars that are too cool to burn hydrogen-are very similar in appearance to red dwarf stars, which are just hot enough to burn hydrogen. Stars, when first formed, contain substantial amounts of the element lithium. All stars but the coolest of the brown dwarfs are hot enough to destroy lithium completely by converting it to helium. accordingly, any star found that contains no lithium is not one of these coolest brown dwarfs.

The argument depends on assuming which one of the following?

(A) None of the coolest brown dwarfs has ever been hot enough to destroy lithium.
(B) Most stars that are too cool to burn hydrogen are too cool to destroy lithium completely.
(C) Brown dwarfs that are not hot enough to destroy lithium are hot enough to destroy helium.
(D) Most stars, when first formed, contain roughly the same percentage of lithium.
(E) No stars are more similar in appearance to red dwarfs than are brown dwarfs.

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f2001290 · Tue May 29, 2007 10:05 am

I will go with B. What's the OA?

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800GMAT · Tue May 29, 2007 12:35 pm

Hi f2001290, can u pls explain how u arrived at B?
Thnkx

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RAGS · Thu May 31, 2007 4:45 am

I think its A
The argument says that coolest brown dwarfs do not destroy lithium , all others do. And concludes that stars that do not contain lithium will not be the coolest brown dwarfs.
So negating A we say that the coolest brown dwarfs were hot at one point in time to destroy lithium then the conclusion will fall apart and we can say that it is possible the stars that do not contain lithium can be coolest brown dwarfs

OA please..........

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Princeton Review · Fri Jun 01, 2007 1:35 pm

I believe that A is the correct answer. The conclusion of the argument is that any star containing no lithium is not one of the coolest brown dwarf. The evidence for the conclusion is that brown dwarfs do not burn hot enough to destroy lithium, and that all other stars do.

The assumption is that the brown dwarf was NEVER hot enough to destroy the lithium. That links the conclusion and the evidence. Watch out for conclusions that are more extreme than the evidence warrants--they'll often have a structure like this.

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800GMAT · Sat Jun 02, 2007 10:41 am

thank you all for the reasoning and the answer...

The OA is A

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