00:01
So i'm going to draw a tree diagram of this situation.
00:03
We have stocks that did much better than average, and that was 25%.
00:10
And then we had 25 % that did much worse than average, and then we had 50 % that did about the same, about the same as average.
00:24
And of the much better, we had those that had a good rating was 40%.
00:32
So this would be 60%, so not good.
00:36
And of those that averaged about the same, we had 20 % of those were considered good buys, and so we would have 80 % that were not considered good.
00:47
And down here we only had 10 % that were considered good buys, and so that would be 90 % were not considered good.
00:54
And we want to find what is the probability, given that we had something that was considered to be a good buy, what was the likelihood that it came from the much better category than average? so we know that means we need to find the probability of much better and good and good divided by the probability of good.
01:24
Now we have three ways we can have good...