Hi Everyone, Let's see if someone here can do a better job than my teacher! I have one of the least helpful stat teachers ever. She told me that I was wrong about the following problem. I am not saying that she is wrong or right, but when I asked her to explain why I was wrong, she told me that I should just use the formula, and she couldn't explain it until I had taken higher level classes. Here is the problem: Each person owns one and only one of the following pets: Dog = 1699 people Cat = 1418 people Bird = 826 people Fish = 504 people Lizard = 233 people Other = 177 people Total People = 4857 Total Pets = 4857 A = Event that a random person owns a Bird or a Fish B = Event that a random person owns a Dog, a Cat or a Bird Given that a randomly selected person owns a Bird or a Fish, what is the probability a randomly selected person owns a dog, a cat, or a bird? I said that the answer would be Bird / (Bird + Fish) = 826/1330 = .621, because we know that the Randomly selected person owns a bird or a fish, and bird is the only shared result of A and B. My teacher said this was wrong, and a formula had to be used to get the right answer, but she refused to go into more depth??? Can someone here please explain what my mistake was? Thanks very much for your help.