"Trevor" wrote in message
...


"David" wrote in message
...
"William Sommerwerck" wrote in message
...

But by not switching doors, you are ignoring the new
information that the
prize has to be behind one of the other two doors....

No, it doesn't. That's not correct.

You are sticking with
your original guess that had only a 1/3 chance of being right.
By
switching
doors, you are including the new information that the prize
has to be
behind
one of the other two doors, and your new chance of winning is
50%.

No, it doesn't. Your new chance of winning is 2/3.

***
This is similar to another puzzle. A couple has two children.
What is the probability that the second is a boy? The couple
then volunteers that they are not both girls. Now what is the
probability the second is a boy?

The first case is 1/2. The second case is 2/3.


Wrong, on a purely statistical basis the first case is 50:50, BB,
BG, GB, or
GG. Two out of four meet the criteria.
The second case is 50:50 Boy or Girl, One out of two meets the
criteria.

snip
Trevor.

The second case is: BB, BG, GB. The couple told you the GG case
does not exist.
Get it now? The goat problem has similar probability outcome
changes.

David