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The bowl contains only white and black balls. What is the

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The bowl contains only white and black balls. What is the [#permalink]

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New post 02 Sep 2008, 05:30
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

The bowl contains only 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 in the bowl
2. If two balls are extracted from the bowl, the probability that both of them are black is 0

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Senior Manager
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Re: probbility [#permalink]

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New post 02 Sep 2008, 05:33
A should be the answer.

1) Probability is 2/3
2) There is only one black ball, but the number of white ones is not known; insufficient
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Re: probbility [#permalink]

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New post 03 Sep 2008, 12:43
I am also agree with 'A'.

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Re: probbility [#permalink]

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New post 03 Sep 2008, 13:00
arjtryarjtry wrote:
The bowl contains only 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 in the bowl
2. If two balls are extracted from the bowl, the probability that both of them are black is 0


Given;
w = the number of white balls in the bowl
b = the number of black balls in the bowl

Prob(Get 1 White) = n(Get White)/n(Get Any ball)
n(Get White) = wC1 = w -------------- (e.g. 3C1 = 3!/(2!*1!) = 3)
n(Get Any ball) = (w+b)C1 = w + b

Therefore, Prob(w =1) = w/(w+b)

1. w = 2b, put this in the equation above
Prob(w=1) = 2b/(2b+b) = 2b/3b = 2/3 SUFF

2. If prob(b = 2) = 0 then there is only 1 black in the bowl. b = 1
no information about white balls therefore INSUFF .

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Re: probbility   [#permalink] 03 Sep 2008, 13:00
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The bowl contains only white and black balls. What is the

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