Complete baloney! The author correctly states that, for probability calculations, “The first—and most important—rule of counting is this: What is everything that can happen? In the “Mrs Smith” problem, given the information provided, everything that can happen is this:
Boy, Girl
Girl, Boy
Boy, Boy.”
The list should include all the DIFFERENT possibilities. Possibilities 1 and 2 are the same for purposes of the problem. Therefore the probability is (close to) 1/2, not 1/3.
No, they’re no different possibilities. You don’t know birth order.
Welcome to probability. Each outcome has an equal possibility - BG, GB. Briggs is right.