Imagine that you have three boxes: one containing two black marbles, another containing two white marbles and a third containing one black marble and one white marble. The boxes were labeled for their contents—BB, WW and BW—but someone has switched the labels so that every box is now incorrectly labeled. You are allowed to take one marble at a time out of any box, without looking inside, and by this process of sampling, you are to determine the contents of all three boxes.