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# A certain jar contains only b black, w white and r red

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Joined: 20 Sep 2007
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A certain jar contains only b black, w white and r red [#permalink]  19 Jun 2008, 21:21
A certain jar contains only b black, w white and r red marbles. If one marble is 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

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Manager
Joined: 24 Apr 2008
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Re: marbles in a jar probability from Gmat prep [#permalink]  19 Jun 2008, 22:28
2
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Ans: A

Target: r/(r+w+b) > w/(r+w+b) if and only if r>w

St1: r/ w+b > w/ b+r -----> w+b /r < b+r / w ---> add 1 on both sides we get

w+b+r / r < b+r+w / w ---> P(r)> P(w) -----suffic

St2: b-w>r ----- Insuffi
Re: marbles in a jar probability from Gmat prep   [#permalink] 19 Jun 2008, 22:28
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