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posted by larry .
A box contains 10 red balls and 20 blue balls. Three balls are selected at random one after the other from the box, without replacement. If the first two balls selected are both blue, what is the probability that the third ball selected is red?

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PsyDAG
P(2 blue balls) = 20/30 * 19/29
P(red ball third) = 10/28
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