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Senior Manager
Joined: 07 Nov 2004
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A couple want to have four babies, for each baby, 50% are [#permalink]
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16 Feb 2005, 00:48
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A couple want to have four babies, for each baby, 50% are male, 50% are female. Ask for the possibility of two boys and two girls?



Manager
Joined: 13 Feb 2005
Posts: 63
Location: Lahore, Pakistan

I think your question is incomplete.....please specify the number of babies



GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5043
Location: Singapore

I assume what you want to ask, is what is the probability of getting 2 girls and 2 boys, and for each child, there is a 50% possibility for either gender.
So what you need is:
BOY AND BOY AND GIRL AND GIRL (independent event)
So P= 1/2*1/2*1/2*1/2 = 1/16



GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5043
Location: Singapore

antmavel, it's been a while since the last time we communicated.
just for a spot of cheekiness, it's "same method as ywilfred" instead of "same method than" (GMAT SC)



VP
Joined: 13 Jun 2004
Posts: 1115
Location: London, UK
Schools: Tuck'08

ywilfred wrote: antmavel, it's been a while since the last time we communicated. just for a spot of cheekiness, it's "same method as ywilfred" instead of "same method than" (GMAT SC)
My verbal skills are terrible, i am really a poor french guy
That's why I only hunt in the Quant forum



Intern
Joined: 19 Feb 2005
Posts: 9

shouldnt it be 3/8
total outcomes... 2*2*2*2 = 16
Our Outcomes
BBGG
BGBG
BGGB
GBBG
GBGB
GGBB
= 6
6/16 = 3/8 ??? whats the OA ?



Director
Joined: 13 Nov 2003
Posts: 789
Location: BULGARIA

Prob is (B+G)^4=(1/2+1/2)^4 and the possible outcomes are:
bbbb=1/16
bggg=4/16
bbgg=6/16
bbbg=4/16
gggg=1/16



SVP
Joined: 03 Jan 2005
Posts: 2233

Antmavel wrote: My verbal skills are terrible, i am really a poor french guy That's why I only hunt in the Quant forum
Huh? If this is the case you should really hunt the Verbal forum more Antmavel.



SVP
Joined: 03 Jan 2005
Posts: 2233

Please read this thread and see if it gives you some light.
http://www.gmatclub.com/phpbb/viewtopic.php?t=14548



SVP
Joined: 03 Jan 2005
Posts: 2233

Read this and see if you could do it again, vprabhala.
http://www.gmatclub.com/phpbb/viewtopic ... 9947#89947



Director
Joined: 21 Sep 2004
Posts: 607

but it doesn't say atleast. it says.. what is the probability of getting 2 boys and 2 girls right Honghu?



Director
Joined: 21 Sep 2004
Posts: 607

there is a difference between atleast and exactly i guess.
following the method.
1none of them are boys(means all girls) one of them is a boy(means 3 girls)
should it be giving 2 boys and 2 girls.
that would be 13/16



Intern
Joined: 27 Jun 2004
Posts: 33

I believe it's 3/8. Use the distribution formula
c(n,k)*p^k*(1p)^(nk).
Thanks HongHu. The theory and examples you've provided in the post above are real useful.



Director
Joined: 21 Sep 2004
Posts: 607

4C2*(1/2)^2*(1/2)^2=3/8
I still don't get hte difference between exactly, atleast etc..
can Honghu please explain..



VP
Joined: 30 Sep 2004
Posts: 1480
Location: Germany

vprabhala wrote: 4C2*(1/2)^2*(1/2)^2=3/8 I still don't get hte difference between exactly, atleast etc.. can Honghu please explain..
exactly means EXACTLY 2 boys and 2 girls in different combinations => bbgg or bggb or bggb, etc..
atleast 1 boy means bggg or bbgg or bbbg or bbbb,... => 4c1*(1/2)^4 + 4c2*(1/2)^4 + 4c3*(1/2)^4 + 4c4*(1/2)^4
atleast 1 boy and 1 girl bggg or bbgg or gggb,... => same way as as it is above



VP
Joined: 13 Jun 2004
Posts: 1115
Location: London, UK
Schools: Tuck'08

3/8*3/8 for me >prob is 9/64 to get exactly 2 boys and 2 girls
what's the OA ? Hong Hu ?



VP
Joined: 25 Nov 2004
Posts: 1483

it is 3/8.
2B and 2G = (4c2+4c2) = 6
total possibilities = 16
2B and 2G= 6/16=3/8



Manager
Joined: 01 Jan 2005
Posts: 166
Location: NJ

Total possibilities = 2*2*2*2=16
Poss of 2 grls and 2 boys
bbgg
bgbg
bggb
ggbb
gbgb
gbbg
=6/16=3/8



Senior Manager
Joined: 07 Oct 2003
Posts: 350
Location: Manhattan

MA wrote: it is 3/8. 2B and 2G = (4c2+4c2) = 6 total possibilities = 16 2B and 2G= 6/16=3/8
I now understand that the answer should be 3/8, however (4c2+4c2)=12, not six...
number of ways of getting two girls out of 4 babies
4c2 = 6
number of ways of getting 2 boys out of remaining 2 boys
2c2 = 1
hence we have (6*1)/(1/2^4) = 3/8
great refresher...



VP
Joined: 13 Jun 2004
Posts: 1115
Location: London, UK
Schools: Tuck'08

HongHu wrote: Antmavel wrote: 3/8*3/8 for me >prob is 9/64 to get exactly 2 boys and 2 girls
what's the OA ? Hong Hu ? Why 3/8*3/8?
I need some sleep....










