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A couple has two children, one of whom is a girl.

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

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New post 23 Apr 2016, 06:24
HKD1710 wrote:
chetan2u wrote:
REDWASP2205 wrote:
chetan2u

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..


Hi chetan2u,

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

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New post 23 Apr 2016, 10:45
HKD1710 wrote:
chetan2u wrote:
REDWASP2205 wrote:
chetan2u

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..


Hi chetan2u,

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?


Hello HKD1710

Please go Through eshan429 's post

probability-217147.html#p1406381

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

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New post 23 Apr 2016, 10:53
Thanks Abhishek009,

I went thru all those solutions and i still did not understand only the following:

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

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

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New post 23 Apr 2016, 10:56
HKD1710 wrote:
Thanks Abhishek009,

I went thru all those solutions and i still did not understand only the following:

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


I hope its clear with you now, in case of any doubt , please feel free to revert ( Because I know P&C and Prob Concepts are very confusing) !!

Happy Preparations

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

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New post 23 Apr 2016, 11:07
Abhishek009 wrote:
HKD1710 wrote:
Thanks Abhishek009,

I went thru all those solutions and i still did not understand only the following:

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


I hope its clear with you now, in case of any doubt , please feel free to revert ( Because I know P&C and Prob Concepts are very confusing) !!

Happy Preparations

Abhishek


Any explanation on that specific part i mentioned would bring clarity. :)
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Re: A couple has two children, one of whom is a girl. [#permalink]

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

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New post 23 Apr 2016, 11:38
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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
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Re: A couple has two children, one of whom is a girl. [#permalink]

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

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New post 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 :)
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http://gmatclub.com/forum/information-on-new-gmat-esr-report-beta-221111.html
http://gmatclub.com/forum/list-of-one-year-full-time-mba-programs-222103.html

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

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

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New post 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

*U = Union

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Re: A couple has two children, one of whom is a girl.   [#permalink] 08 Sep 2017, 19:36

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