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# One Girl - One Boy

### #1

Posted 12 July 2007 - 05:03 PM

They have two kids, one of them is a girl, what is the probability that the other kid is also a girl.

Assume safely that the porbability of each gender is 1/2.

### #2

Posted 12 July 2007 - 05:48 PM

### #3

Posted 12 July 2007 - 07:41 PM

lol but the title says "One Girl - One Boy" so maybe there's a 0% chance the second kid is a girl because its a boy?

### #4

Posted 12 July 2007 - 10:18 PM

It's a lousy puzzle.

Its not, wait for the reasoning till someone gets the right answer!

### #5

Posted 12 July 2007 - 10:44 PM

you said kid, which can refer to a goat

and you just said married couple

### #6

Posted 12 July 2007 - 11:12 PM

are these people or animals, because you never said child

you said kid, which can refer to a goat

and you just said married couple

Yes, we are talking about human-beings here, this is no lateral thinking puzzle.

Good job rookie, these spoiler tabs are excellent!

### #7

Posted 12 July 2007 - 11:18 PM

first you have one girl then the next needs to be a guy

### #8

Posted 12 July 2007 - 11:20 PM

probability is 1/2

or 1 out of 2

they have 2 children

1 out of two is a girl then the other 1 out of two has to be a boy

(edit: I suck at spelling so I fixed it)

### #9

Posted 12 July 2007 - 11:27 PM

oops i forgot

probability is 1/2

or 1 out of 2

they have 2 children

1 out of two is a girl then the other 1 out of two has to be a boy

(edit: I suck at spelling so I fixed it)

The probability of having a girl or a boy is same and is 1/2. i.e. same as saying if a fair coin is tossed then odds of getting a head is 50% and getting a tail is also 50%. Hope this makes is more clear, take another digg @ the question!

### #10

Posted 13 July 2007 - 05:38 AM

Comparing a coin toss is a common mislead. A single coin toss is of course 50/50. But 2 consecutive tosses is 50/50 for the first, and 25/75 for the second. Taken as a set (as you must in a family), you cannot discount the total probability by looking at the single toss.

Much like this:

I have 3 boxes (a - b - c).

2 have nothing in them.

1 has a million dollars.

If you guess the correct one, you get the money.

You pick one.

Out of the remaining 2, I show you that one is of course empty.

I give you the option of changing your answer.

Do you have better, worse, or the same odds if you DO change?

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