1. If you get a black ball of the same color every time, after 50 times, there will be only white in the box! ! This will be white when you take it out and put it in! Everything that can be left is white.

2. If everything is black and white, it will be all black after 100 times! So take out a pair of balls and put in a white ball! Take a white ball and cut it off, which is equivalent to three black balls becoming one black ball! There are 34 black balls left (int (100/3)+(100 mod 3)), then it becomes 12, then 4, then 2. So there is only one white ball left.