A woman has two kids. One is a boy. What are the odds the other is a boy?

That is true. I believe out of every birth, 2/3 chance = female ; 1/3 chance = male, or something or the like. I don't remember the exact %. So if that's correct, 33% is the true answer.

What the hell are you smoking?

	X	X
X	girl	girl
Y	boy	boy

ARGGGGGGGGGGGGGGGGGGGGGGGRRRRRRRRRRRRRRRRRRHHHHHHHHHHHHHHHH!!!!!!!

Wow, it's my pet hate!

It is NOT 100%, 33% or 25%. The answer is 50%.

The events of "having child 1" and "having child 2" are independent events. What happened the first time will not affect what happens the second time. So, we are told that the first one is a boy. So that one is a boy. Now, we are worried about the second one. What happened with the first one is completly irrelevant. There is a 50% chance of it being a boy. 50% chance of it being a girl. 50% is the answer! I'll do the mathmatical working later if needed.

Have some of you not done probability in school yet?

That is true. I believe out of every birth, 2/3 chance = female ; 1/3 chance = male, or something or the like. I don't remember the exact %. So if that's correct, 33% is the true answer.

[citation needed]


Also, I guess that there really is a reason that some people use junk 30%/ 10% scrolls before using the one they want to o_o
They actually think that it helps......

You flip a coin. You get heads.

You flip another coin. What's the chance of it being heads? Still 50%.

You flip a coin. You get heads.

You flip another coin. What's the chance of it being heads? Still 50%.

But it's actually 33% chance to get heads in a row.

That would be 25%.

50% chance for the first, 50% chance for the second (.5*.5).

You're asking about the chance of just the second.

But it's actually 33% chance to get heads in a row.

Its 50% to get heads the first time, 25% to get it again, 12.5% percent to get it three times. If the problem was like the baby situation where a man flips two coins and one of them is heads, then it's 33%

This isn't about coins.

This isn't about coins.

It's the same thing though o_o

This question would work if rephrased as such:

A woman has two kids. At least one is a boy. What are the odds that they are both boys?

It's the same concept.

It's generally assumed that a kid has a 50/50 chance of being either sex. In that case, any kid has a 50% chance of being male. Even if you know one kid is male, that in no way affects another.

If a family has three daughters (and the father doesn't have fucked up sperm), then the chance of the fourth child being male is still 50%.

Let me try the example I gave on irc.

First I gave the coin example.

And then I said "Okay, a woman has a child. It is a boy!"
Then I said "She's about to have another one. What is the chance that the new child she has is a boy?"

So, answer my question

This isn't about coins.

Consider the four possibilities for having two children:

B/B
B/G
G/B
G/G

Consider the four possiblities for flipping two coins:

H/H
H/T
T/H
T/T

That said, first one is H?

H/H
H/T

Second one is H?

H/H
T/H

Still 50% chance either way.

Okay, 2 coins. Still 33% chance to get two heads in a row. I don't know what you guys are on. 50% isn't the correct answer.

How is it 33%?

Okay, 2 coins. Still 33% chance to get two heads in a row. I don't know what you guys are on. 50% isn't the correct answer.

Um... the probably of getting two heads in a row would be 25%. But that's a different question from the two children one.

Two heads in a row is H/H yes?

So therefore we can rule out the combination of T/T and we're left with:

H/T
T/H
H/H

Which is 1/3rd or 33%.

What the hell are you smoking?

	X	X
X	girl	girl
Y	boy	boy

If you're looking at that as chromosomes, individually, yes, 50% would be the right answer. But technically, the correct answer is 33%.

As Opeth stated about flipping coins, here's how it works. Let's say you aim to get 2 heads out of '2' coins. Most people would say, that's a 50% rate! ... Wrong.

Flip #1: Head / Tail, you get Head. 50%
Flip #2: Head / Tail, you get Head again. So you actually divide it up by 2. Making it a 25% success rate of landing 2 'heads' out of 2 coins.

To explain more in depth, 50% * .5 or 50% / 2

Lern2mathpls.

As for the 33% ratio, that's because the chances of anyone giving birth to males is just 33%. The chances of females are 66%. If you read some Biology book or maybe some anatomy books, perhaps it'll list it on there, but I read a lot of sources that says it's 33%.

PS: Also, if you flip 4 coins, what are the chances that they will all be 'head'?

50% * .5 * .5 * .5 * .5 = answer, making it 3.125%

Um... the probably of getting two heads in a row would be 25%. But that's a different question from the two children one.

Okay, from irc I know you've said 33% for the kids problem and 25% for the coins one, both of which are wrong...

But they are the same concept. The answer has to be the same. It's just simple probability. There are 2 outcomes, with an equal chance of each event. Both are done twice in a row. What's different?

So there's about twice as many females on the planet compared to males?

I wish that was true, though.


I've heard somewhere that there's a 50.5% chance of getting a boy because newborn boys die more commonly than newborn girls. Though I don't recall any sources to this.

It's like scrolling a weapon with a 30% scroll in-game, you tell me. ;]

As for the 33% ratio, that's because the chances of anyone giving birth to males is just 33%. The chances of females are 66%. If you read some Biology book or maybe some anatomy books, perhaps it'll list it on there, but I read a lot of sources that says it's 33%.

http://en.wikipedia.org/wiki/Gender_imbalance

I know it's pineappleing Wikipedia, but seriously, how the hell can you think twice as many female babies are born as male babies?

Edit: Here's a better source. http://education.yahoo.com/reference/fac...23e6LGecYF

Two heads in a row is H/H yes?

So therefore we can rule out the combination of T/T and we're left with:

H/T
T/H
H/H

Which is 1/3rd or 33%.

But if you aren't given that one of them is heads, then you can't rule out T/T

edit: actually in sicnarf's example, it's still 50% because you are given that the first coin is heads, so you rule out T/T and T/H. So we're left with:

H/T
H/H

Still a different question though.