We answered that here just recently.
I chanced upon this puzzle on some math site.I have some doubts about the sloution supplied on that site.
I wanna see whether others will supply answers that agree with that supplied.
Here's the puzzle:
The first box has two white balls. The second box has two black balls. The third box has a white and a black ball. The boxes have been labeled but all labels are wrong!
You are allowed to open one box, pick one ball at random, see its color and put it back into the box, without seeing the color of the other ball.
How many such operations are necessary to correctly label the boxes?