Boy or girl puzzle

Sorry that this is disjointed, i thought i was posting after an earlier point in the thread. i'm new to this and will learn how to quote-the post i am responding to. Anyhow you all should get the gist of what i am thinking and or asking.

I f you get 50% when you know it is the eldest son, the same can be calculated if you knew it was the youngest son ( you would rule out GG and BG in this case).

So why do you even need that info, its already there. Without being told, I know that the chances of a boy being either the eldest or the youngest out of two children is 100%. Both the eldest and the youngest son solutions end in the 50% not the 33.33% chance.

In other words how can you not have the information you need to get to 50%.

Perhaps this reasoning will help: consider two tossed coins with the outcomes hidden under cups. You are guaranteed at least one of the coins is "heads." I hope you will find it easily reasoned that the chance of both being "heads" is 1/3. (HH, HT, TH) A cup is removed and you are shown that one of the coins is "heads." Obviously, the probababiliy that both are "heads" is then 1/2. The difference is not knowing the result of either coin and knowing the result of one coin.

Edit: spelling

Quote: 1call2many

In other words how can you not have the information you need to get to 50%.

I posted the answer to that last night in the other thread you started on this same topic.

Quote: Doc

I posted the answer to that last night in the other thread you started on this same topic.

Hi Doc, I read your response last night, posted to the "Mr. Smith" thread. I meant to post to that thread, but it sank below the recent posting list and I found this thread on a search. Yes, your answer is spot-on. I just thought I would present something based more on intuitive reasoning that rigorous proof.