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GMAT Prep : Probability

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Source: — Data Sufficiency |
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by Geva@EconomistGMAT » Mon Oct 04, 2010 3:08 am
Nifty trick for this difficult question:

Add +1 to both sides of the inequality in (1). You get:

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

combine the 1 with the fractions on either side:

r+(b+w) / b+w > w+(b+r) / (b+r)

Note that the numerators are now the same r+b+w (the total number of options). Cross multiply to put that quantity in the bottom and make for a proper probability function:

(b+r)/ w+b+r > b+w / w+b+r
It follows that r>w, and the answer is yes.

Stat. (2) is insufficient with plugging in - you can find two opposing scenarios, where r is both smaller and greater than w, depending on the value of b.
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by Skywalker » Mon Oct 04, 2010 5:37 am
Geva

Thanks a lot. With exams just a week away...anything that I 'm not able to solve gets me all worked up. After looking at your solution, the sum seems so simple....
Hope these things strike a chord when the D day comes.

cheers
StAy HuNgry sTay fOOlisH
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by Geva@EconomistGMAT » Mon Oct 04, 2010 5:51 am
Skywalker wrote:Geva

Thanks a lot. With exams just a week away...anything that I 'm not able to solve gets me all worked up. After looking at your solution, the sum seems so simple....
Hope these things strike a chord when the D day comes.

cheers
You're more than welcome. :)
Good luck on your test.
Geva
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