Each of 25 balls is either red, blue, or white and has a : DS Archive
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Each of 25 balls is either red, blue, or white and has a

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Manager
Joined: 08 Nov 2005
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Kudos [?]: 20 [0], given: 10

Each of 25 balls is either red, blue, or white and has a [#permalink]

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29 Sep 2009, 09:03
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Q1) Each of 25 balls is either red, blue, or white and has a number from 1 to 10. If one ball is selected at random, what is the probability that the ball is either white or has an even number on it?

(1) Probability that the ball is both white and has an even number = 0
(2) Probability that the ball is white minus probability that the ball has an even number = 0.2
Manager
Joined: 11 Sep 2009
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Kudos [?]: 341 [0], given: 6

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29 Sep 2009, 12:27
We are looking for the probability that a ball is either white or even, P (W or E).

P (W or E) = P(W) + P(E) - P(W and E)

Statement 1:Probability that the ball is both white and has an even number = 0

This statement conveys the fact that P(W and E) = 0. We're still left with: P (W or E) = P(W) + P(E). Therefore Statement 1 is insufficient.

Statement 2: Probability that the ball is white minus probability that the ball has an even number = 0.2

This statement conveys that P(W) - P(E) = 0.2. Since we don't have any other piece of information, this is clearly insufficient as well.

Looking at the Statements Together .

We have two pieces of information:

1) P(W or E) = P(W) + P(E)
2) P(W) - P(E) = 0.2

So P(W) = P(E) + 0.2 and as a result P(W or E) = 2P(E) + 0.2. The probably is we still don't know the probability of the ball being drawn being even. Therefore this is still insufficient.

Therefore the correct answer is E.
Re: DS probablity   [#permalink] 29 Sep 2009, 12:27
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