No, that's not what this is about. Probability means this: "in X tries, how likely is it for Y to happen". The ambiguity here is this: what is the set of X? Is

No, that's not what this is about. Probability means this: "in X tries, how likely is it for Y to happen". The ambiguity here is this: what is the set of X? Is the set of all families with two children at least one boy, or the set of all families with 2 children of which you have determined one is a boy. Those are different sets. It doesn't matter how you discovered the information. The apparent paradox is all grammar and set description. Think of it this way - you want to test this out and actually run this experiment? Great! What's the experiment? Are you starting with all families with 2 children, or all families which 2 children at least one boy. >> How I know the information about on data point one affected the likelihood of an unrelated one No, it doesn't.