03 Oct '10 14:09

A different version of a puzzle I put up some time ago.

I have 4 identical bags each containing 2 balls.

1 bag has 2 white balls

1 bag has 2 black balls

2 bags have 1 black and 1 white

I pick a bag at random and take out a ball. It is black.

I have 4 identical bags each containing 2 balls.

1 bag has 2 white balls

1 bag has 2 black balls

2 bags have 1 black and 1 white

I pick a bag at random and take out a ball. It is black.

**What is the probability of the other ball being black?**