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drawing a white ball?

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by sanju09 » Sat Oct 22, 2011 4:16 am
In a 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?
(A) 1/5
(B) ¼
(C) 3/10
(D) 1/3
(E) ½
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by Anurag@Gurome » Sat Oct 22, 2011 4:23 am
sanju09 wrote:In a 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?
The probability of drawing a red ball, returning it, and then drawing a white ball = (Probability of drawing a red ball)*(Probability of drawing a white ball)

Hence, 1/10 = (1/5)*(Probability of drawing a white ball)
Hence, Probability of drawing a white ball = (1/10)/(1/5) = 1/2

The correct answer is E.
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by user123321 » Sat Oct 22, 2011 4:24 am
assuming x red and y green balls.
x/(x+y) = 1/5

(x/(x+y))*(y/(x+y)) = 1/10
substituting first equation
we get y/(x+y) = 1/2 which is nothing but prob. of drawing white ball

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by vaibhavgupta » Sat Oct 22, 2011 4:26 am
sanju09 wrote:In a 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?
(A) 1/5
(B) ¼
(C) 3/10
(D) 1/3
(E) ½
IMO E thought they asked for green one
whats the OA?
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by sanju09 » Sat Oct 22, 2011 4:43 am
Signify P as the probability of drawing a white ball from the jar. The probability of drawing a red ball is 1/5. The probability of drawing both measures is 1/10 so, 1/5 x P = 1/10.
Therefore P = [spoiler]½.


OA is E[/spoiler]
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