Hi everybody.(adsbygoogle = window.adsbygoogle || []).push({});

Once more, I need your help.

The following is a problem that appears in Rohatgi's "An introduction to Probability and Statistics":

"Each of n urns contains four white and six black balls, while another urn contains five white and five black balls. An urn is chosen at random from the (n+1) urns, and two balls are drawn from it, both being black. The probability that five white and three black balls remain in the chosen urn is 1/7. Find n."

My first guess would be that n=6, but the solution given in the book is n=4.

Someone can tell me if I am wrong or there is a mistake in the book ?

Thanks.

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# It seems easy, but I don't get it

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