SOLUTION: A box contains 3 red and 7 green marbles. If 9 marbles are drawn without replacement, what is the expected number of red marbles?
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Question 1155530: A box contains 3 red and 7 green marbles. If 9 marbles are drawn without replacement, what is the expected number of red marbles?
Answer by greenestamps(13203) (Show Source): You can put this solution on YOUR website!
When 9 marbles are drawn without replacement, there is one marble left.
The probability that 3 red marbles are drawn -- i.e., that the remaining marble is green -- is 7/10; similarly, the probability that 2 red marbles are drawn is 3/10.
The expected number of red marbles drawn is then
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