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  4. A bag contains 4 white and 6 black balls. Three balls are drawn at random from the bag. Let X be the number of white balls, among the drawn balls. If σ2 is the variance of X, then 100 σ2 is equal to

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Q. A bag contains 4 white and 6 black balls. Three balls are drawn at random from the bag. Let $X$ be the number of white balls, among the drawn balls. If $\sigma^2$ is the variance of X, then $100 \sigma^2$ is equal to

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Solution:

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$ \sigma^2=\sum X^2 P(X)-\left(\sum X P(X)\right)^2=\frac{56}{100} $
$ 100 \sigma^2=56$