DixieDean said:seeing as we're a little short of topics at the moment I thought I'd get everyone's brain going with this teaser....
A man has two children. One of them is a boy. What's the probability that the other one is a boy?
yes....can you explain why?championship_here_we_come said:
DixieDean said:yes....can you explain why?championship_here_we_come said:
NeverBeatDaveHiggins said:I'm gonna stick with 50-50, since the gender of the second child is not conditional on the gender of the first. It's always luck of the draw which sperm makes it.
DixieDean said:NeverBeatDaveHiggins said:I'm gonna stick with 50-50, since the gender of the second child is not conditional on the gender of the first. It's always luck of the draw which sperm makes it.
If a man has two children, he could have had:
first a boy, then a girl - BG
first a boy, then another boy - BB
first a girl, then a boy - GB
first a girl, then another girl - GG
These are the only possible ways in which a man can have had 2 children, and they are all equally probable.
We know that at least one of the children is a boy. That cuts out just one of the 4 possibilities listed above - GG - leaving 3 possibilities: BG, GB, BB (each of which, as we've seen, is equally likely).
Of those 3, only one - BB - satisfies the condition that the other child is a boy as well. So the answer is 1 in 3, or 33.3% (.3 recurring to be precise).
So well done CHWC, you kinda got there!
championship_here_we_come said:is theory 1/3 is correct however in practice we all know this is incorrect as some families will have all boys and no girls or the other way round
so in practice it is still 50/50 as i orginally siad and so did NeverBeatDaveHiggins
NeverBeatDaveHiggins said:Ah so the phrasing of the question is the real question. I'm right when talking about a second child yet to be born, you're right in the very specific circumstance of talking about two children already born and we're told the gender of one of them (NOT the first one, just one of them), but not the gender of the other.
NeverBeatDaveHiggins said:I'm gonna stick with 50-50, since the gender of the second child is not conditional on the gender of the first. It's always luck of the draw which sperm makes it.