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GMAT Prep?? (Prob) Pract2

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by dferm » Tue May 13, 2008 3:40 pm
A certain jar contains only b black marbles, w white marbles, and r red marbles. If one marble is to be chosen at random from the jar, is the probability that the marble chosen will be red greater than the probability that the marble chosen will be white?

(1) r/b+w > w/b+r
(2) b-w > r

Please Help...

thanks..
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Source: — Data Sufficiency |
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by codesnooker » Wed May 14, 2008 10:23 pm
Answer is (A).
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by netigen » Wed May 14, 2008 10:44 pm
Rephrase the DS question:

Is R>W?

Lets look at A

Is am assuming this r/b+w > w/b+r means r/(b+w) > w/(b+r )

r/(b+w) > w/(b+r )
rb+r^2>bw+w^2
rb-bw>w^2-r^2
b(r-w)>(w-r)(w+r)

if (r-w)>0 then b>(w-r)(w+r)/(r-w) or b>-(w+r)
if (r-w)<0 then b<(w-r)(w+r)/(r-w) or b<-(w+r)

A is insufficient

Lets look at B now

b-w>r
or b>r+w

B is insufficient

If we take both A and B then we know that r-w>0 or r>w and hence C is sufficient
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by codesnooker » Wed May 14, 2008 11:00 pm
If condition 1 means: (r/b)+w > (w/b)+r then 100% (A) is alone sufficient, however if it means r/(b+w) > w/(b+r) then ans is (C).

Dferm, what is the correct question? I guess in future, at least you can take of to post the question in correct format.

Thanks
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