Banachs matchcbox problem-Probability

Posted by kangkan on Feb 24, 2014; 10:51am
URL: http://discussion-forum.276.s1.nabble.com/Banachs-matchcbox-problem-Probability-tp7584906.html

Mr. Stephan kept two matchboxes, one in each pocket. Each box
contained exactly n matches. Whenever he wanted a match he reached at
random into one of his pockets. When he found that the box he picked
was empty, what is the probability that the other one has exactly k
matches

I am unable to make sense of the wikipedia solution.