SOLUTION: A box contains 30 balls: 20 are red and 10 are blue. Five balls are selected at random, without replacement. What is the probability that four of them are red? What if the five bal

Question 267588: A box contains 30 balls: 20 are red and 10 are blue. Five balls are selected at random, without replacement. What is the probability that four of them are red? What if the five balls are selected at random with replacement (i.e, a selected ball is put back in the box before the next selection is made)?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A box contains 30 balls: 20 are red and 10 are blue.
Five balls are selected at random, without replacement.
What is the probability that four of them are red?
P(r = 4) = (20C4*10C1)/30C5 = 4845/27405 = 0.1768
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What if the five balls are selected at random with replacement (i.e, a selected ball is put back in the box before the next selection is made)?
P(r = 4) = 5C4(2/3)^4(1/3) = 0.3292
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Cheers,
Stan H.
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