There are n balls in a box. Each ball is of a different color. At each iteration, you draw 2 balls at random, and paint the second ball so that it's the same color as the first; then you replace the balls. You keep repeating this until all the balls in the box are of the same color. What is the expected number of iterations?
- Via Quora
There is a nice thread on math overflow to discuss this problem here. Thanks to Sudeep Kamath for pointing this out.