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Eventually, just one ball is left in the container. What color is it?

+1 vote

A container contains 75 white balls and 150 black ones.

Next to the container is a large pile of black balls.

The coach asks one of the players to remove the balls from the container, one at a time, according to the following strange rule: He has to remove two balls from the container at random. If at least one of the balls is black, he places it on the ball-pile and drops the other ball, no matter what color, back in the container.

If both balls are white, on the other hand, he discards both of them and removes one black ball from the pile and drops it in the container.

At each turn of this procedure, the container has one less ball in it. Eventually, just one ball is left in the container. What color is it?

posted Jul 10 by Vikram Luthra

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1 Answer

0 votes


According to the first procedure one black ball is removed from the container when white+black or black+black combination is removed. White ball gets back to the container if one of two is white.
According to second procedure 2 white balls removed and replaced with one black ball. The white balls can be removed in pairs only. The odd white ball will always be the last one.

answer Jul 10 by Hanifa Mammadov

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