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Each of the 25 Balls

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stanbinev
 Post subject: Each of the 25 Balls
 Post Posted: Wed Sep 09, 2009 11:47 pm 
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Students


Posts: 3
Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it. If one ball is selected at random from the box, what is the probability that the selected ball will either be white or have an even number painted on it?

1) The probability that the ball will both be white and have an even number painted on it is 0.
2) The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2

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So we know that the probability of an even number is 0.5, therefore as per 2) the probability of the ball being white is 0.7, i.e. 7 of the balls are white. How do I determine the sufficiency of each argument however? That's where I get stuck. I know it's not C because the two statements contradict each other. Thoughts?
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sunny.jain
 Post subject: Re: Each of the 25 Balls
 Post Posted: Thu Sep 10, 2009 1:56 am 
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Students


Posts: 111
Well..how can u say that P(even number ) = 0.5

all 25 balls has number printed on them...

we dont know how many balls has even number printed on them ?

P(W U E) = P(W) + P(E) - P(W A E)

1) P(W A E) = 0
Still we need P(W) + P(E)
So Insufficient.

2) P(W) - P(E) = 0.2
Still not Sufficient.

Combining these two, I still think its not sufficient. I think answer should be E.
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RonPurewal
 Post subject: Re: Each of the 25 Balls
 Post Posted: Sat Sep 26, 2009 1:45 am 
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ManhattanGMAT Staff


Posts: 7146
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