Black and White Balls Puzzle You have 20 white and 13 black balls in a bag. You pull out 2 balls one after another. If the balls are of same color, then you replace them with a white ball – but if they are of different color, you replace them with a black ball. Once you take out the balls, you do not put them back in the bag – so the balls keep reducing. What would be the color of the last ball remaining in the bag. Solution: Black How? So the solution is very simple,the trick is in the Question itself.Let me give you hint again "You pull out 2 balls one after another. If the balls are of same color, then you replace them with a white ball – but if they are of different color, you replace them with a black ball." So, the black balls would always be odd in numbers – either you remove 2 together or remove 1 and add 1 – so they remain odd always. So, the last ball in the bag would be a black ball only.