Question 27
Three boxes contain three balls each: one has 1 white and 2 black, one has 2 white and 1 black, and one has 3 white. Their labelled lids are rearranged so none correctly describes its box. Mike chooses a box and removes balls at random, observing their colours without replacing them. What is the smallest number of balls he needs to remove to guarantee determining every box’s contents?
