"Vic Smith" wrote in message
...
On Thu, 29 Jan 2009 20:29:09 GMT, Wizard of Woodstock
wrote:

On Thu, 29 Jan 2009 15:14:05 -0500, "Eisboch"
wrote:


"Wizard of Woodstock" wrote in message
...


Math illiteracy affects 8 out of every 5 people.


Speaking of math illiteracy.

My son, also bored with winter, hit me with this classic "Monty Hall"
challenge last night.
Goes something like:

=============================================== ==

A contestant is on "Let's Make a Deal". She is told that behind one of
three curtains there is a new car. Behind the other two curtains are
dirty
old goats.

She picks a curtain. Before it is opened, one of the other curtains is
opened to reveal some dirty old goats.

She is then given the opportunity to change her mind about which
remaining
curtain she thinks the car is behind.

What should she do?

=============================================== =

Surprisingly, I chose what is considered to be the correct answer.
I'll let those that have never heard of this think about it and decide
for
themselves.

It's simple. There are two doors left which leaves three choices. Of
the three choices, two probabilities exist that she wins the car by
switching her choice.

She switches her choice to increase the probability of winning the
car.

Doesn't make sense.
She made her choice when the odds were 2:1 against her.
Since one curtain was eliminated, the odds are now 1:1.
Changing her choice won't change the odds.
The odds changed when the first curtain was opened.
Flip a coin 10 times and it comes up heads each time.
What are the odds of heads on the 11th flip?
Same as they were on the first flip. 1:1.
Or even money for you real gamblers.
Of which Galactic guys don't qualify.
Unless you're wagering quateros on warpsnerk lightbeam racing.

--Vic



Tom was correct, although I am not sure why.

Her probability of winning increases from 33.3% to 66.6% by changing her
initial pick. The majority of people do not get this right and don't
understand why.

This is a classic mathematical probability exercise that has been bashed
about for years by everyone from math PhD's to grammar school whiz kids.

When she first picked a curtain, she had a 2 in 3 chance of being wrong.
That didn't change after the first curtain with goats was opened. But it
does change if she changes her choice, and it can only increase her chances
of being correct.

Here's another explanation:

http://mathforum.org/dr.math/faq/faq.monty.hall.html

Eisboch