__Description__

**A cloth bag contains a single red pool ball.**

A second pool ball is chosen at random in such a way that it is equally likely to be a red or a yellow ball. The ball is added to the bag, the bag is shaken, and a ball is drawn at random.

The withdrawn ball proves to be a red.

__Puzzle__
What
is the probability that the ball remaining in the bag is also a red?

Check the solutions page for the correct answer.

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