Something I finally understand
I’ve heard of the question about the probabililty of a second child being a boy before – it’s a standard mathematical puzzle to get you to think about conditional probabilities (similar to the Monty Hall problem)
Finally I think I understand it. I always knew there were two candidate answers – 50/50 or 2/3 – but despit eknowing 2/3 was right (or so I thought) was never completely comfortable with it. So here goes:
It’s either 50/50 or 2/3 depending on whether the parent picked the child they told you the sex of randomly or not.
If they picked it randomly and then said “hey look – it’s a girl” then the probability of a boy being left is 50-50, as the picking of the first child was independent of the sex of the second child.
However, if they deliberately picked a girl to tell you the sex of, then they are skewing the probabilities in favour of leaving a boy behind (as they have removed the possibility of picking a boy from the probability space), hence increasing the probability to 2/3.
No related posts.
Tags: coding horror, monty hall, probability