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An urn has n balls and we take balls from it with replacement until each ball has been drawn at least one. X denotes the number of draws required. What is the expected value and variance of X? I think X is at least n, is it true? And how should I find the expected value of it?

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    $\begingroup$ This is known as the coupon collector problem, $\endgroup$ – lulu Nov 12 '18 at 15:29
  • $\begingroup$ Thank you so much $\endgroup$ – werlless Nov 12 '18 at 15:36

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