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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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New post 24 Jul 2009, 13:23
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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 grater than the probability that the marble chosen will be white?

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


Thanks a lot. I saw this on a GMATPrep sample exam.
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Re: (Help) DS Problem #2: Please take a stab, anyone! [#permalink]

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New post 24 Jul 2009, 21:16
Consider r=9, w=8, b = 7

Probability for red marble = 9/24
Probability for white marble = 8/24

r/(b+w) = 9/15
w/(r+b) = 8/16

So r/(b+w) > w/(r+b) and probability of red marble is greater than white

Let us assume r=8, w=9, b=7

Probability for red marble = 8/24
Probability for white marble = 9/24

r/(b+w) = 8/16
w/(r+b) = 9/15
So r/(b+w) < w/(r+b) and probability of red marble is less than white


2)
b> r+w
We cannot decide whether r is greater or w is geater among r and w

So 1 alone is sufficient and answer is 'A'

Please post OA
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Re: (Help) DS Problem #2: Please take a stab, anyone! [#permalink]

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New post 24 Jul 2009, 21:49
The answer is A.

Also, from what you just outlined before saying the answer was A, weren't you implying that 1 was insufficient?

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Re: (Help) DS Problem #2: Please take a stab, anyone! [#permalink]

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New post 24 Jul 2009, 22:03
I mentioned two scenarios to say that when red marbles are greater or less than white 1 holds good. So the answer was "A" only
Re: (Help) DS Problem #2: Please take a stab, anyone!   [#permalink] 24 Jul 2009, 22:03
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A certain jar contains only b black marbles, w white

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