Question 14
A box contains ten black balls and ten white balls and there are no balls outside the box. In each step Mickey is allowed to do one of the two things. (a) He may take a white ball and a black ball from the box and place them outside. (b) If there is at least one black ball outside the box, he may take a white ball from the box and place it outside, and return a black ball from outside into the box. After six steps Mickey counts the number of balls outside the box. How many possible answers are there?