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.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

**Physics Forums | Science Articles, Homework Help, Discussion**