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Probability

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by danjuma » Mon Sep 20, 2010 2:57 pm
2. 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 to be selected at random what is the probability that the ball selected will either be white or have an even number painted on it?

a.The probability that the ball will both be white and have an even number painted on it is 0

b. The probability that the ball will have an even number painted on it is 0.2
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Source: — Data Sufficiency |
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by Gurpinder » Mon Sep 20, 2010 4:57 pm
(E)

question: white or have an even number on it.

(a) talks about white AND even number. we dont know anything about either one. hence insufficient.

(b) prob of even # = .02. the prob that it will not be even # is .08. hence alone is insufficient.

together:

since we don't know the individual probability from (a), 2 does not really help.

.02 for even #s
but we dont know about the white.

hence (e)
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
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