In a country where everyone wants a boy(A country like India), each family continues having
babies till they have a boy.
After some time, what is the proportion of boys to girls in the country?
Note that probability of having a boy or a girl is same.
Answer:-
Assume there are C number of couples so there would be C boys. The number of girls can be calculated by the following method.
Number of girls = 0*(Probability of 0 girls) + 1*(Probability of 1 girl) + 2*(Probability of 2 girls) + …
Number of girls = 0*(C*1/2) + 1*(C*1/2*1/2) + 2*(C*1/2*1/2*1/2) + …
Number of girls = 0 + C/4 + 2*C/8 + 3*C/16 + …
Number of girls = C
(using mathematical formulas; it becomes apparent if you just sum up the first 4-5 terms)
The proportion of boys to girls is 1 : 1.
Another Explanation -
Let us take an example that in a country there are 40 couples and considering same probability of a girl and a boy 25 of them will have a boy as their first child.
Here B = 20 G = 20 (B = No.of Boys, G = No. of Girls)
Now for the rest of 20 couples 10 of them will have a Boy as their second child and rest 10 will have girl again as their second child.
So here B = 30(20 + 10)
G = 30(20 + 10)
The no. of boys and girls will always be same. The answer is shocking but true.
Please leave your comments below for any query.....
After some time, what is the proportion of boys to girls in the country?
Note that probability of having a boy or a girl is same.
Answer:-
Assume there are C number of couples so there would be C boys. The number of girls can be calculated by the following method.
Number of girls = 0*(Probability of 0 girls) + 1*(Probability of 1 girl) + 2*(Probability of 2 girls) + …
Number of girls = 0*(C*1/2) + 1*(C*1/2*1/2) + 2*(C*1/2*1/2*1/2) + …
Number of girls = 0 + C/4 + 2*C/8 + 3*C/16 + …
Number of girls = C
(using mathematical formulas; it becomes apparent if you just sum up the first 4-5 terms)
The proportion of boys to girls is 1 : 1.
Another Explanation -
Let us take an example that in a country there are 40 couples and considering same probability of a girl and a boy 25 of them will have a boy as their first child.
Here B = 20 G = 20 (B = No.of Boys, G = No. of Girls)
Now for the rest of 20 couples 10 of them will have a Boy as their second child and rest 10 will have girl again as their second child.
So here B = 30(20 + 10)
G = 30(20 + 10)
The no. of boys and girls will always be same. The answer is shocking but true.
Please leave your comments below for any query.....
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