Urn Puzzle

Urn Puzzle

An urn contains 75 white balls and 150 black balls. Next to the urn is a large pile of black balls.

Again and again, someone removes a pair of balls from the urn. If either ball is black, then a black ball is placed on the pile, and the other ball is returned to the urn. If both balls are white, then they are discarded, and a black ball is taken from the pile and returned to the urn.

On every turn, there is one less ball in the urn. What color is the last marble in the urn?

2 Responses

  1. Gagan says:

    last ball remaining has to be white because the number of white balls is always decreasing by an even number and initially they are 75 in number
    so in the last step, 1 white ball has to remain

  2. there wud be two balls remaining…
    one is white and other one is black.