Wanna debate a math problem?
Post Reply
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
23-02-2012, 02:42 PM (This post was last modified: 23-02-2012 02:54 PM by germanyt.)
Wanna debate a math problem?
http://en.wikipedia.org/wiki/Boy_or_Girl_paradox

I'm reading this and banging my head on my desk. Someone please explain to me how the answer to question 2 is 1/3? It doesn't make any sense.



Regardless of which sex the older child is the answer is 1/2 for questions 1 and 1/4 for queston 2. Since there are only 2 sexes and probablilty for both is half then the only possible answer is 1/2 and 1/4. They are improperly using the number of outcomes to determine their answer. BB, BG, GB, GG gives you 4 different possibilities. If the first child is a boy then the probably of the second being a girl is still 50% since the chances of it coming out of the womb a boy or girl are 50%.



WTF at 1/3?



edit
Now I'm confused from reading it so many times.



edit
If changes when you ask the probability of 'both being the same' or the 'other one the same'.


OK start over

Mr. Jones has two children. The older child is a girl. What is the probability that both children are girls?

Answer is either 50% based not on possible outcomes but on the probability of having a girl or boy. The children you had before have no effect on the sex of the new child. Or it is 25% based on the probability of halving 2 children the same sex.

I'm leaning towards 50%.

Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?

This one makes me lean 25%.

Someone help me understand why.

“Whenever you find yourself on the side of the majority, it's time to pause and reflect.”

-Mark Twain
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 02:54 PM
RE: Wanna debate a math problem?
It's the same premise as the "coin flip".

Q: If you flip a coin, how often will it land on heads?

Intuitive answer is 50%; however, the correct answer is 33.3% because a coin has three sides. It's logically unlikely but technically correct.

At least... this is what I gather from it... I'm probably wrong, though.

[Image: vjp09.gif]
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 02:55 PM
RE: Wanna debate a math problem?
(23-02-2012 02:54 PM)kingschosen Wrote:  It's the same premise as the "coin flip".

Q: If you flip a coin, how often will it land on heads?

Intuitive answer is 50%; however, the correct answer is 33.3% because a coin has three sides. It's logically unlikely but technically correct.

At least... this is what I gather from it... I'm probably wrong, though.

But you would also have to consider the likelyhood of the coin landing on it's edge. Surface area, wind, etc. In the OP the subjects are just as likely to have a boy as a girl.
I think I've decided that if you ask what sex the 'other' child is, the answer is 50%. If you ask what the chances of having the same sex are the answer is 25%.

Either way, 1/3 is never an answer.

“Whenever you find yourself on the side of the majority, it's time to pause and reflect.”

-Mark Twain
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 03:05 PM (This post was last modified: 23-02-2012 03:12 PM by FSM_scot.)
RE: Wanna debate a math problem?
From a genetic standpoint, Both should be 50%, as there are only two genders. There are certain conditions where an individual has an extra sex chromosome, such as Klinefelter syndrome, but those individuals are classed as male, as they they have a Y chromosome.

Even when Factoring in conditions like that, it shouldn't change the probability of the second child being the same sex as the child who's gender was already known.
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 03:18 PM (This post was last modified: 24-02-2012 12:52 AM by kim.)
RE: Wanna debate a math problem?
1.) From all families with 2 children, at least one of whom is a boy, a family is chosen at random.
one of the families has a boy
one of the families has a girl
one of the families has a child -either a boy or a girl but not specified .

The consideration discussed is the family chosen ... not whether it's a boy or a girl.
They choose 1 family from 3 choices. In other words: 1/3rd.

I think in the end, I just feel like I'm a secular person who has a skeptical eye toward any extraordinary claim, carefully examining any extraordinary evidence before jumping to conclusions. ~ Eric ~ My friend ... who figured it out.
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 03:41 PM
RE: Wanna debate a math problem?
(23-02-2012 03:18 PM)kim Wrote:  1.) From all families with 2 children, at least one of whom is a boy, a family is chosen at random.
one of the families has a boy
one of the families has a girl
one of the families has a child -either a boy or a girl but not specified .

The consideration discussed is the family chosen ... not whether it's a boy or a girl.
They choose 1 child from 3 choices. In other words: 1/3rd.


But the answer to these two questions is 25%.

Mr. Jones has two children. The older child is a girl. What is the probability that both children are girls?
Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?

It's the same as asking it like this.

Mr. Jones has two children. What is the probability that both children are girls?
Mr. Smith has two children. What is the probability that both children are boys?



If they ask what the probability of the other (not both) child is the answer is 50%.

“Whenever you find yourself on the side of the majority, it's time to pause and reflect.”

-Mark Twain
Find all posts by this user
Like Post Quote this message in a reply
23-02-2012, 04:09 PM
RE: Wanna debate a math problem?
I'm sorry... I didn't read beyond the sentence you wrote:

Quote:Someone please explain to me how the answer to question 2 is 1/3? It doesn't make any sense.

I thought this was the only part you couldn't figure out?

You're gonna make me read more?
It's your problem, why do I have to do all the work? Huh

I think in the end, I just feel like I'm a secular person who has a skeptical eye toward any extraordinary claim, carefully examining any extraordinary evidence before jumping to conclusions. ~ Eric ~ My friend ... who figured it out.
Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes kim's post
23-02-2012, 04:23 PM
RE: Wanna debate a math problem?
(23-02-2012 04:09 PM)kim Wrote:  It's your problem, why do I have to do all the work? Huh

Because you're a woman. Now, get back in the kitchen!

I swear... women these days... think they can talk back to a man. What's this world coming to? Flipping 2012. Modern times crap. Still can't believe they can vote. I swear... this country is going to hell in a hand basket. Next thing we know we'll be allowing men to marry men. Jesus just needs to come back.

GIT OFF MY LAWN!!!!

Stupid kids.

[Image: vjp09.gif]
Find all posts by this user
Like Post Quote this message in a reply
[+] 2 users Like kingschosen's post
23-02-2012, 04:26 PM
RE: Wanna debate a math problem?
Boys are stupid.

boy--> [Image: 13.gif]

I think in the end, I just feel like I'm a secular person who has a skeptical eye toward any extraordinary claim, carefully examining any extraordinary evidence before jumping to conclusions. ~ Eric ~ My friend ... who figured it out.
Find all posts by this user
Like Post Quote this message in a reply
[+] 2 users Like kim's post
23-02-2012, 04:36 PM
RE: Wanna debate a math problem?
All possible combinations : BB BG GB GG

The older child is a girl rules out BB and BG leaving 2 possibilities so the chance 50%.

One of the children is a boy rules out GG leaving 3 possibilities so the chance is 33.3%

'The world holds two classes of men: intelligent men without religion, and religious men without intelligence.' - Abdallah al-Ma'arri
Find all posts by this user
Like Post Quote this message in a reply
[+] 5 users Like daylightisabadthing's post
Post Reply
Forum Jump: