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: probability....revised..!!  ( 7292 )
« : October 12, 2007, 12:34:56 AM From Rajesh»


Ronald and Michelle have two children. The probability that the first child is a girl, is 50%. The probability that the second child is a girl, is also 50%. Ronald and Michelle tell you that they have a daughter.

What is the probability that their other child is also a girl?

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« #1 : October 12, 2007, 02:41:52 PM From spazinvader»

Is it 50%?
I don't get it.It seems very simple to me.
So i think i have missed something.
Is my answer right?
« #2 : October 12, 2007, 05:24:44 PM From Shrinidhi»

It is also 50% as probability of one child doesn't depend on the probability of the other child.
« #3 : October 14, 2007, 02:14:03 PM From Rajesh»

no guys....50% is not correct ans .....!!!
« #4 : October 26, 2007, 11:37:20 PM From Poonam»

Even I feel that the probability is 50%. The couple has confirmed that the first child is a girl. Also there is no constraints for the second child. Hence the probability remains same.... 50%.
« #5 : October 28, 2007, 11:11:17 PM From spazinvader»

Is the answer 0%?
What is the probability that their other child is also a girl?

He hasn't mentioned that the child is the first or second right?

Ronald and Michelle tell you that they have a daughter.
So i have taken that Ronald and Michelle told that they have only one daughter.
Since they have only one daughter,the another child should be their son.
So the probability of the other child being a girl is 0%.
« #6 : October 29, 2007, 11:54:16 AM From Rajesh»

There are four possibilities for two children:

     first child:    second child:
1    girl             girl
2    girl             boy
3    boy           girl
4    boy           boy

The fourth possibility drops out, because Ronald and Michelle have a daughter. Therefore, three possibilities remain, of which in one case the other child is also a girl. So, the probability is 1/3 (about 33%).
« #7 : October 29, 2007, 07:54:39 PM From spazinvader»

A query to you Rajesh.
The possibilities are
1)Boy Boy
2)Boy Girl
3)Girl Boy
4)Girl Girl

In this,as per their statement,the condition 1 is ruled out.
Now as per them, the statement is "they have a daughter".
So the second condition and third conditin comes under same na?
I mean,they have a girl and then a boy as well as they have a boy and girl makes them have one girl only right?
So both the states make only one possibility right?
And having a girl makes another possibility.
So the possibility is
1/2=50% right?
« #8 : October 30, 2007, 01:56:19 PM From Rajesh»

no dear....both will be consider as different cases....first girl then boy and first boy then girl are different cases...though it seems same as they are talking "they have a daughter"....actually all the 4 cases r different...
« #9 : October 31, 2007, 09:01:22 PM From spazinvader»

Still i am not convinced Rajesh.Let me tell my confusion clearly.
If the coupke have two children and it is concerned with how many daughters are there for the couple,the probabilities are
1.Having No daughter
2.Having 1 daughter
3.Having 2 daughters

In this,it is already given as they have a daughter.So the first probability is ruled out.Hence the probabilities are
1.Having 1 daughter
2.Having 2 daughters

So the posssibility of having their other child as daughter comes as 50% right?
If we have taken as the above mentioned cases,all the cases will comes under these conditions right?
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