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# A certain jar contains only b black marbles, w white

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Intern
Joined: 23 Jun 2009
Posts: 47

Kudos [?]: 28 [0], given: 6

A certain jar contains only b black marbles, w white [#permalink]

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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.

Kudos [?]: 28 [0], given: 6

Manager
Joined: 10 Jul 2009
Posts: 164

Kudos [?]: 117 [0], given: 8

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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'

Kudos [?]: 117 [0], given: 8

Intern
Joined: 23 Jun 2009
Posts: 47

Kudos [?]: 28 [0], given: 6

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24 Jul 2009, 21:49

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

Posted from my mobile device

Kudos [?]: 28 [0], given: 6

Manager
Joined: 10 Jul 2009
Posts: 164

Kudos [?]: 117 [0], given: 8

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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

Kudos [?]: 117 [0], given: 8

Re: (Help) DS Problem #2: Please take a stab, anyone!   [#permalink] 24 Jul 2009, 22:03
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