Before you on a table are 3 closed boxes, one full of RED chips, one full of BLUE chips, and one with a mix (half-and-half) of RED and BLUE chips. The boxes are labeled "RED," "BLUE," and "Mixed," but each label is WRONG (on the incorrect box). You are to blindly and randomly pick ONE chip out of any box of your choice and then re-assign the labels correctly (upon seeing the picked chip). Can it be done, and if so from which box would you select?
Pick from box labeled "Mixed" -- whatever you get, red or blue, will be the proper label for that box (since it can't actually be mixed), and then the other two follow easily.
from:
http://math-frolic.blogspot.com/2012/07/friday-puzzle.html