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Re: A bowl contains white and black balls. What is the [#permalink]

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06 Nov 2007, 09:59

I will go with A

1. Since there are twice as many white balls as black balls.
Probability to extract a white ball will be 2/3

2. "If two balls are extracted from the bowl, the probability that both of them are black is 0"
This is only possible when either there is no black ball or either 1 black ball. So we cannot determine the probability of extracting a white ball...

Re: A bowl contains white and black balls. What is the [#permalink]

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06 Nov 2007, 10:09

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sportyrizwan wrote:

I will go with A

1. Since there are twice as many white balls as black balls. Probability to extract a white ball will be 2/3

2. "If two balls are extracted from the bowl, the probability that both of them are black is 0" This is only possible when either there is no black ball or either 1 black ball. So we cannot determine the probability of extracting a white ball...

Am I correct ?

Yup sporty. Just one clearification.

I assume that sufficiency of A is pretty clear.

As far as B is concern, black ball cant not be 0 since question states that
A bowl contains white and black balls

So it is clear that there is 1 black ball.
Why B is insufficient?

assume there are only 1 black and 1 white ball- probability to extract a white ball from the bowl= 1/2

Now assume there are 3 white balls and 1 black ball - probability to extract a white ball from the bowl is 3/4

Re: A bowl contains white and black balls. What is the [#permalink]

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08 Jan 2008, 11:31

1

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A S1 gives 2/3- suffi S2 gives, prob both black=0, which says that there is only one black ball in there. So, the no of white balls can be anything, so we cant find prob of white= s2 not suffi

Re: A bowl contains white and black balls. What is the [#permalink]

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28 Sep 2009, 11:07

A bowl contains white and black balls. What is the probability to extract a white ball from the bowl?

1. There are twice as many white balls as black balls 2. If two balls are extracted from the bowl, the probability that both of them are black is 0

Soln.

Statement 1 alone is sufficient. Assuming that there are x black balls. Hence 2x white balls. Thus probability of drawing a white ball is = 2x/3x = 2/3

Statement 2 alone is not sufficient. From this statement we cannot guess the number of white and black balls present.

Re: A bowl contains white and black balls. What is the [#permalink]

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04 Jan 2012, 12:54

Clearly A. Statement 1 gives us the probability as 2/3 and statement 2 does not gives us any information regarding the number of white balls or the total number of balls.
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Re: A bowl contains white and black balls. What is the [#permalink]

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04 Jan 2012, 13:25

The stem can be rephrased as w/(w+b)?

1. w = 2b. Sufficient by substitution 2. This means that there is only one black ball. Let t = total, so black = 1 and white = t - 1. This implies (t-1)/[(t-1)+1] = (t-1)/t. We don't know the total, so insufficient

A.
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DS - If negative answer only, still sufficient. No need to find exact solution. PS - Always look at the answers first CR - Read the question stem first, hunt for conclusion SC - Meaning first, Grammar second RC - Mentally connect paragraphs as you proceed. Short = 2min, Long = 3-4 min

Re: A bowl contains white and black balls. What is the [#permalink]

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26 Jul 2014, 06:34

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Re: A bowl contains white and black balls. What is the [#permalink]

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17 Aug 2015, 20:53

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