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Another probability question

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by mjjking » Wed Feb 25, 2009 6:47 am
In a blue jar there are red, white and green balls. The probability of drawing a red ball is 1/5. The probability of drawing a red ball, returning it, and then drawing a white ball is 1/10. What is the probability of drawing a white ball?

1/5.
½.
1/3.
3/10.
¼.
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Re: Another probability question

by sureshbala » Wed Feb 25, 2009 7:04 am
mjjking wrote:In a blue jar there are red, white and green balls. The probability of drawing a red ball is 1/5. The probability of drawing a red ball, returning it, and then drawing a white ball is 1/10. What is the probability of drawing a white ball?

1/5.
½.
1/3.
3/10.
¼.
Let the total number of balls be N and W be the number of white balls.

Given that 1/5 x W/N = 1/10

So W/N = 1/2

Hence the probability of drawing a white ball is 1/2
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by bluementor » Wed Feb 25, 2009 7:07 am
Prob(Red) = 1/5

Prob(Red AND White) =Prob(Red) And Prob (White)
1/10 = (1/5)*Prob(white)

Therefore Prob(White) = 5/10 = 1/2.

Choose B

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by mygmat.2009 » Wed Feb 25, 2009 12:01 pm
Following the binomial probability theory we can say:

[2 choose 2] * (Prob Red)^1 * (Prob White)^1 = 1/10

==> 1 * (1/5) * ( X ) = 1/10

==> X = 1/2
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