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Question
Two cards are drawn successively with replacement from a well shuffled pack of 52 cards. Find the probability distnbution of the number of spade cards.
Chart
Sum
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Solution
Let X denote the number of spades in a sample of 2 drawn cards from a well shuffle pack of 52 cards.
Then, X can take the values 0, 1, 2.
Now, P(X = 0) = P(no spade)
= `(""^39C_2)/(""^52C_2)`
= `741/1326`
= `19/34`
P(X = 1) = P(one spade card)
= `(""^13C_1 xx ""^39C_1)/(""^52C_2)`
= `507/1326`
= `13/34`
P(X = 2) = P(both cards are spade)
= `(""^13C_2)/(""^52C_2)`
= `78/1326`
= `1/17`
Thus, the probability distribution of X is given by
| X | P(X) |
| 0 | `19/34` |
| 1 | `13/34` |
| 2 | `1/17` |
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Variance of a Random Variable
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