I need help on this one:
There are two bags, each of them contain $n$ balls.
The first bag contains only white balls. The second bag contains only black balls.
Pick one black ball and input it to first bag. Then choose one ball from first bag randomly and and throw out it. Repeat this process while second bag is not empty.
What is probability that last selected ball from first bag is white?
I guess there are some recurrence formula for this probability...