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But knowing One of them is a girl, shouldn't we remove BG from the possible cases.

No, Because we just know that one of them is G.. here the order is important but we are not given the order but just that one is a G.. If it said the first one is a G, then yes we would have had ONLY two cases GB or GG..

This one is crucial for me to understand. whether a boy is first and girl is second or boy is younger than girl or vice versa--WHY do we consider BG, GB as two cases instead of ONE case only. We are not arranging here.

I looked at the responses from Bunuel and others on original post too but i still have this doubt. Could you please explain this?

Hi,

I would relate this Q to two different Q.

1) Ways to pick two books out of 4 books randomly? 4C2..

2) Ways to pick two books out of 4 books one after another? this will be 4C2 *2!

Our Q is similar to the 2nd case
_________________

But knowing One of them is a girl, shouldn't we remove BG from the possible cases.

No, Because we just know that one of them is G.. here the order is important but we are not given the order but just that one is a G.. If it said the first one is a G, then yes we would have had ONLY two cases GB or GG..

This one is crucial for me to understand. whether a boy is first and girl is second or boy is younger than girl or vice versa--WHY do we consider BG, GB as two cases instead of ONE case only. We are not arranging here.

I looked at the responses from Bunuel and others on original post too but i still have this doubt. Could you please explain this?

IMHO, I don't feel you need to consider younger /older in this case. The chances of having a twins ( Boy and Girl) in a single delivery can not be rejected.

Both Boy and Girl may be born at the same time, we need to consider only the probability of having only 2 daughters ( They may be twins as well - Born on the same day)

Younger / Elder daughter is not important in this case , we simply restrict ourself to a female child (daughter)

Happy Preparations

Abhishek _________________

Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

Re: A couple has two children, one of whom is a girl. [#permalink]

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23 Apr 2016, 11:25

HKD1710 wrote:

WHY do we consider BG, GB as two cases instead of ONE case only. We are not arranging here.

BG = Boy takes birth Before Girl

GB = Girl takes birth before Boy

PS: I know I might be contradicting my own theory of twins , but it is crucial to understand it this way. Even twins born on the same day may be few minutes apart

Does it help you anyway ? _________________

Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

Any explanation on that specific part i mentioned would bring clarity.

Hi, Do not get into kids as B or G,try with another example say there are two different flavours of icecream - V and C.. 50% chances that one can pick either and eat.. we know he ate two and one was surely a V.. what is the probabilty that he had two vanillas, V.. he could have had VC or CV or VV
_________________

Re: A couple has two children, one of whom is a girl. [#permalink]

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23 Apr 2016, 11:42

Abhishek009 wrote:

HKD1710 wrote:

WHY do we consider BG, GB as two cases instead of ONE case only. We are not arranging here.

BG = Boy takes birth Before Girl

GB = Girl takes birth before Boy

PS: I know I might be contradicting my own theory of twins , but it is crucial to understand it this way. Even twins born on the same day may be few minutes apart

Does it help you anyway ?

well neither we need to apply the twin or age or any other theory. lets put it this way:

I am told that my neighbour has two child. one is girl another may be boy or girl. I went to my neighbour's house. here are the total case:

1. a boy opens the door (then other child as we already know is girl) hence - BG. 2. a girl opens the door. (then other child could be boy or girl )- hence (GB or GG)

This is why we have these three cases.

GG is favorable out of three. so 1/3.
_________________

Re: A couple has two children, one of whom is a girl. [#permalink]

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23 Apr 2016, 11:44

chetan2u wrote:

HKD1710 wrote:

Any explanation on that specific part i mentioned would bring clarity.

Hi, Do not get into kids as B or G,try with another example say there are two different flavours of icecream - V and C.. 50% chances that one can pick either and eat.. we know he ate two and one was surely a V.. what is the probabilty that he had two vanillas, V.. he could have had VC or CV or VV

Thanks chetan. Your assistance helps! Kudos
_________________

Re: A couple has two children, one of whom is a girl. [#permalink]

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08 Sep 2017, 14:01

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A couple has two children, one of whom is a girl. [#permalink]

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08 Sep 2017, 19:36

TimeTraveller wrote:

Sample space = {bb,bg,gb,gg}

Favourable event = {gg}.

Since it's given that one of the child is a girl, the new Sample Space = {bg,gb,gg}.

So, probability = 1/3. Ans (C).

Hi Bunuel, If we consider above method, does it mean that the given probability of either boy or girl being 50% is not required to solve the problem? And also can you please tell, the given probability translate into which of the below equations?:- P(B U G)= 0.5 or P(B) = P(G)= 0.5