I have a simple riddle

Did you choose from a sample of families which have at least one boy or from the general population then set the question?

Shoebacca wrote:

I hate problems like this. It's clearly a 50% chance. I laugh at all these probability snobs who think "B/G" and "G/B" are two separate options.

Wrong. Kartelite and others are right. The is the Monty Hall riddle re-written.

Probabilty, like most maths questions requires one to construct the problem correctly first in order to to solve it. The question was not "what is the probability of each subsequent birth?" That is 50 percent. The question is "I have two kids, one of them is a girl, what is the probability that the other is a boy". The one door is opened for you (girl). What is behind the closed door? The answer is 2/3 chance boy. 1/3 chance girl.

"In no other branch of mathematics is it so easy for the experts to blunder as in probability." - Martin Gardner.

yes, it's obvious wrote:

2/3

2nd post wins again. Correct answer just three minutes after start of thread.

Why did you all pollute the thread after that perfect post?

malmo wrote:

Wrong. Kartelite and others are right. The is the Monty Hall riddle re-written.

Probabilty, like most maths questions requires one to construct the problem correctly first in order to to solve it. The question was not "what is the probability of each subsequent birth?" That is 50 percent. The question is "I have two kids, one of them is a girl, what is the probability that the other is a boy". The one door is opened for you (girl). What is behind the closed door? The answer is 2/3 chance boy. 1/3 chance girl.

"In no other branch of mathematics is it so easy for the experts to blunder as in probability." - Martin Gardner.

Doesn't this logic rest upon the false assumption that having a boy and having a girl are equally likely events? Gender isn't a coin flip. It's slightly skewed in favor of boys. The math doesn't seem to take this into account.

it is infinite you can define yourself as any gender. also the election was rigged at first it wasnt but when trump won it was so i am mad

You are correct, however, you're arguing a finer point, Mister Pedant.

I'm still confused as to how probability is applicable to something that has already been decided. Before a baby is conceived, there is a certain probability that it will be a boy and a certain probability that it will be a girl. But we're talking about an individual who already exists. At this point, the individual is either male or female. No probability involved.

malmo wrote:

105/100 wrote:

Doesn't this logic rest upon the false assumption that having a boy and having a girl are equally likely events? Gender isn't a coin flip. It's slightly skewed in favor of boys. The math doesn't seem to take this into account.

You are correct, however, you're arguing a finer point, Mister Pedant.

We need a model that takes sperm swimming speeds into account. I'll get to work on that.

Let's think about this wrote:

How many siblings you have? Sisters or brothers? Same question for your spouse?...any twins in the family? Or was infertility drugs involved?

Need little bit more details please...

^^^This is what no one is considering. The paradox assumes four equally weighted outcomes, one of which (two boys) can be eliminated.

However, that assumption is incorrect because it ignores the specific father's genetic predisposition toward siring girls or boys.

It's the probability of you finding out that the child is a specific gender then.

105/100 wrote:

malmo wrote:

You are correct, however, you're arguing a finer point, Mister Pedant.

We need a model that takes sperm swimming speeds into account. I'll get to work on that.

Sounds like that will involve a lot of "research" on your part ;)

105/100 wrote:

Doesn't this logic rest upon the false assumption that having a boy and having a girl are equally likely events? Gender isn't a coin flip. It's slightly skewed in favor of boys. The math doesn't seem to take this into account.

Come on, go ahead and do the math. 2/3 is close enough.

If I said only one is a girl than you would be correct. I do see the ambiguity in the phrasing. Should have said at least one is a girl for more clarity.

Mojo Jerkin wrote:

its just obvious wrote:

I am very surprised so many had so much trouble with this. Let me restate the problem exactly as I stated it, "I have two kids, one is a girl. What is the probability that the other kid is a boy?"

The problem is very clearly stated. I have two kids, one is a girl, what are the chances the the other child is a boy?

Lets look at all the combinations of my two kids:

Boy-Girl

Girl-Boy

Girl-Girl

Boy-Boy

Since one child is a girl, the Boy-Boy option is eliminated which leaves three options.

The chances are 1/3.

Close, but the answer is 2/3. If you eliminate the Girl-Girl combination, you are left with:

BG

GB

GG

Then, you can take one of the G's out of each combination since you know one of the kids is a girl. That leaves you with 2B's and 1 G.

did I ask it correctly?

I have a total of two offspring one of those two has been gender identified as a female . What is the probability that remaining child is a boy?

its just obvious wrote:

I have two kids, one is a girl. What is the probability that the other kid is a boy?

After looking at this again, my original answer is correct and the question is not ambiguous and there is only one correct answer. Everyone saying 2/3 is clearly wrong and not thinking clearly.

Lets say you interpret the question to mean that out of the two kids only one is a girl. Well if you interpret the question that odd way, the probability that the kid "other" than the girl would be a boy is 100%. The answer could never be 2/3.

The question is pretty implicit that at least one is a girl and you have to figure out the probability of the sex of the other.

To say I have two kids and only one is a girl whats the sex of the other one is not a riddle.

End of thread. 2/3 is wrong on all counts.

malmo wrote:

Shoebacca wrote:

I hate problems like this. It's clearly a 50% chance. I laugh at all these probability snobs who think "B/G" and "G/B" are two separate options.

Wrong. Kartelite and others are right. The is the Monty Hall riddle re-written.

Probabilty, like most maths questions requires one to construct the problem correctly first in order to to solve it. The question was not "what is the probability of each subsequent birth?" That is 50 percent. The question is "I have two kids, one of them is a girl, what is the probability that the other is a boy". The one door is opened for you (girl). What is behind the closed door? The answer is 2/3 chance boy. 1/3 chance girl.

"In no other branch of mathematics is it so easy for the experts to blunder as in probability." - Martin Gardner.

Wrong. Hardloper already explained, and I elaborated, that this is the Monty Hall problem fatally misstated. There are no "doors," the OP does not present a starting scenario of 4 equally likely possibilities and then invite you to eliminate one of them leaving three. This scenario starts with given information and only two possibilities, the likelihood of which can't be determined. One can't infer "one of them is a girl" to be providing the same information as a Monty Hall door-opening.

For example, suppose OP was Monty reading off a card that said "state how many children you have and the gender of the oldest." Then he's not saying "one (or the other) is a girl," but "one (specifically) is a girl." This eliminates two, not one, of the 4 possible distributions, leaving the unknown at .5. This is an equally valid premise to the given information as if we had asked if one were a girl, and been told that one (but not which one) indeed was. The unspecificity of the latter is what the "monty hall"-ness of this riddle depends on, but it ironically fails to state the unspecificity specifically enough and fails.

The correct answer is there's not enough information to assign a probability, though you can arguably interpret "one" as written and say 100%, as a mathematician does tend to say "at least one" when that is what is meant.

We're in agreement that it could not be 2/3.Although one literal interpretation of the question could lead one to say 100% chance of a boy, the context of the question in this riddle has a clear meaning. One is a girl what is the probability that the other child is a boy with options being either a boy or girl.Any other interpretation would mean the question is not a riddle. I have a boy and a girl. What's the sex of the one not the girl.

I think I get what you're saying but I still disagree. Let me propose a somewhat analogous thought experiment, and I'll try to avoid any jargon about probability spaces and whatnot.

Say that we have a large urn with 100 pairs of marbles stuck together. There are 100 blue marbles, and 100 red marbles. For simplicity, let's just say that the distribution is the expectation from random sampling:

25 pairs of 2 blue marbles

25 pairs of 2 red marbles

50 pairs of 1 blue marble, 1 red marble

Now, say that you come along to Bob, who is holding a pair of marbles that came from the urn, and he says (with the marbles hidden from your view) that there is at least one blue marble. The question you ask yourself is, what is the probability that the other marble is red?

The problem that I believe you are suggesting is that Bob's comment may not be strictly conditioned on whether or not he holds a blue marble. For example, if we knew that Bob always said "I am not holding a blue marble" if he didn't have one, and "I have at least one blue marble" when he did, I think that you'd agree that the conditional probability that the other marble is red should be 2/3.

HOWEVER, you're trying to go a level deeper and considering the situation that Bob, upon inspecting the marbles after picking them out, may have a different decision rule. For example, he may say "I have at least one red marble" whenever at least one was red, and he will only say "I have at least one blue marble" when BOTH of them are blue. In this situation, there would be a 0% chance that they are both blue.

Since we don't have any information about when Bob will say what, it is impossible for us to assign a probability to the other marble being red. Could you confirm this is your reasoning? I've come up with a proof that shows even in spite of this, the probability is still 2/3, but the margin of this post is too narrow to contain it so I'll post it a bit later on.

OP has proved himself to be a full retard. He couldn't even get the answer to his riddle right and then continues to defend his idiocy.