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# A certain jar contains only B black marbles, W white

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A certain jar contains only B black marbles, W white [#permalink]

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02 Aug 2009, 13:37
00:00

Difficulty:

(N/A)

Question Stats:

100% (00:00) correct 0% (00:00) wrong based on 0 sessions

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A certain jar contains only B black marbles, W white marbles, and R red marbles. If one marble is taken out of the jar, is the probability that a red marble is chosen greater then the probability that a white marble is chosen?

(1) R/(B + W) > W/(B + R)

(2) (B - W) > R

Can't figure out how to solve algebraically

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Intern
Joined: 02 Aug 2009
Posts: 3
Schools: McCombs '17
Re: Difficult probability Question (at least for me!) [#permalink]

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02 Aug 2009, 14:30
1
To tell whether or not red is more likely to be chosen we need to know if there are more red marbles or white marbles. Plugging in random numbers is likely to be the best way to solve the problem.

If B=1, R=5, W=10, then we will have 5/(1+10) > 10/(1+10) or 5/11 > 10/11. Obviously, this isn't true. So R is unlikely to be smaller than W.

If we do it again, B=1, R=5, W=2, then we will have, 5/(1+2) > 2/(1+5) or 5/3 > 2/6. This is true so (1) is sufficient to tell us that there are more red marbles than white marbles.

For (2) (B-W) > R doesn't tell us anything about the relationship between W and R because the size of B will interfere in determining whether or not R or W is larger.

Hopefully that helped.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: Difficult probability Question (at least for me!)   [#permalink] 02 Aug 2009, 14:30
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