345 replies to this topic

[skale]

Ok, so Teanchi and Beanchi are a married couple (dont ask me whose he and whose she)!

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.

Spoiler for solution

Ofcourse its not 1/2 else would make it a lousy puzzle...

Spoiler for solution

Ans: 1/3

This is a famous question in understanding conditional probability, which simply means that given some information you might be able to get a better estimate.

The following are possible combinations of two children that form a sample space in any earthly family:
Girl - Girl
Girl - Boy
Boy - Girl
Boy - Boy

Since we know one of the children is a girl, we will drop the Boy-Boy possibility from the sample space.
This leaves only three possibilities, one of which is two girls. Hence the probability is 1/3

[mdsl]

It's a lousy puzzle.

[unreality]

its 1/2, so its a lousy puzzle...

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?

[skale]

It's a lousy puzzle.

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

[savagegamer90]

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

[skale]

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.

Spoiler for solution

Its a counter-intutive yet simple conditional probability puzzle!

Good job rookie, these spoiler tabs are excellent!

[savagegamer90]

the other child has to be a boy,
first you have one girl then the next needs to be a guy

[savagegamer90]

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)

[skale]

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!

[imtcb]

The answer is 25%. Before they had children the probability for a girl first is 50%. The probability for a girl second is 50%. BUT, to have 2 girls the probability moves to half of half, or 25%.

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?

Spoiler for solution

Better. The first guess you have a 1 in 3 chance of being right. Once I remove one, your odds move up to 2 in 3 by selecting the OTHER box, because it would have been like selecting the 2 boxes you didn't pick.

If I had offered for you to trade your ONE pick for the TWO you didn't pick, before showing one was empty would you?