Interesting theory Mr Mathematician but in reality....

I caught a bit of 'More or Less' on BBC Radio 4* whilst driving today.

There was a very interesting question being debated (stick with me here I don't expect you to do the math!):

If I have a son born on a Tuesday what is the probability of my second child being a son.

The discussion started around the probability of a second child being a son regardless of the day the first was born. The clear answer to which is 1/3.

However, once you start factoring in the day, the answer was 13/27 or was it.....

...a clever Mr Mathematician reasoned that if you had a line of fathers and asked those with 2 children to all stand up (yes I followed thus far),

and then ask those with a boy to remain standing (yes, I can see this working),

then ask those with a boy born on a Tuesday to remain standing (whooooaaaaa there pardner).....

..this is where I lost the thread, you see I reckon most men need a boot (in the posterior) to remember a birthday date let alone the actual day of the week it occurred on, so any theory that involved suggesting a man could recall (without wifey present) the day of the week a child was born lost it's street cred for me

.....so whilst I believe he argued for 1/3 still rather than 13/27, I felt he was missing a major link in the chain but then that's theorising for you.

Want to correct me?!

* listening for the more sedate !