Yes, you are correct. I got lazy as it's 1/2 on both choices so it doesn't effect the final answer.
Bob
]]>Many thanks for your assistance!
]]>I think you can do this using Bayes theorem but, as I can never be bothered to learn it, I prefer to make a probability tree diagram.
Working from left to right, we have the initial set up of 10 blacks and x white. Then either a black or white is added shown by the two branches.
Then we choose a ball which may be black or white. So a further two branches are shown for each of the branches already added.
The final outcomes are shown as 'its black' given 'black' and so on.
As we know the final ball is black we only have two branches to consider: P(b|b) and P(b|w). So I think the answer is
Hope that helps,
Bob
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