Probability of having boy
The proportion of boys to girls is 1 : 1 (Shocked?!!!!)
This is a very simple probability question in a software interview. This question might be a little old to be ever asked again but it is a good warm up.
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.
Event of getting 2 girls may be independent of each other, but here we are talking about probability of occurring that event.
The possible outcomes are: (B for boy and G for girl)
1: B B
2: B G
3: G B
4: G G
Here, probability of getting 2 girls is 1 out of 4 events.
It will always be 1:1 for large number of couples…
Take any number as couples N e.g. 1028.
There will be 512 boys & 512 girls at first delivery….. (1:1)
Couples with Boy stops reproducing & 512 couples with Girls take another chance.
There will be 256 boys & 256 girls in second chance…..(1:1)
256 Couples with Boys stop reproducing & 256 Couples with 2 Girls Now will take another chance….
There will be 128 boys & 128 girls in third chance………(1:1)
128 Couples with Boys stop reproducing & 128 Couples with 3 Girls Now will take another chance….
There will be 64 boys & 64 girls in fourth chance………(1:1)
and ratio will continue till everyone has a boy each………………….then at end there will be N boys & N-1 girls…
So ratio will be N:N-1 which is 1:1 in case of large sample size of N.
sorry,mathematically it is not correct. according to you probability of two girls is (1/2*1/2) and so on.
NO IT IS INCORRECT BECAUSE THE EVENT OF HAVING 2 GIRLS IS INDEPENDENT OF EACH OTHER SO IT CAN’T BE 1/4.
SAME IS THE LOGIC FOR 3 GIRLS, 4 GIRLS. KINDLY REPLY ON THIS FACT.
The answer is given in the question:
Assuming probability of having a boy or a girl is the same, then after a long time, there will be equal numbers of boys and girls.
Why should anyone think that decisions about when to start or stop having children has any effect on their gender?
More puzzles to try-
- 3 + 3 = 3 5 + 4 = 4 1 + 0 = 3 2 + 3 = 4 ...Read More »
- Five puzzleFry ship’s pirates have obtained 100 gold coins and have to divide up the loot. The pirates are all ...Read More »
- There are 10 stacks of 10 coins each. Each coin weights 10 gms. However, one stack of coins is defective ...Read More »
- Dr.Willam wants to operate for three different persons who were wounded. But he had only two surgical gloves. There is ...Read More »
- Which clock works best? The one that loses a minute a day or the one that doesn’t work at all?Read More »
- In the gear arrangement, To which one will the needle touch, 1 OR 2Read More »
- A man leaves his house in the morning to go to office and kisses his wife. In the evening on ...Read More »
- Which letter replaces the question markRead More »
- A bridge will collapse in 17 minutes. 4 people want to cross it before it will collapse. It is a ...Read More »
- A devotee goes to three temples, temple1, temple2 and temple3 one after the other. In front of each temple, there ...Read More »
- There is a perfectly accurate analog watch with hour, minute, and second hands. How many times a day do all three ...Read More »
- Four days are there which start with the letter ‘T‘. I can remember only two of them as “Tuesday , Thursday”. ...Read More »
- Two fathers took their sons to a fruit stall. Each man and son bought an apple, But when they returned ...Read More »
- A farmer is taking her eggs to the market in a cart, but she hits a pothole, which knocks over ...Read More »
- In the middle of the confounded desert, there is the lost city of “Ash”. To reach it, you will have ...Read More »
- Solve this logic sequence puzzle by the correct digit- 8080 = 6 1357 = 0 2022 = 1 1999 = ...Read More »
- Jasmine, Thibault, and Noah were having a night out and decided to order a pizza for $10. It turned out ...Read More »
- A murderer is condemned to death. He has to choose between three rooms. The first is full of raging fires, ...Read More »
- Some numbers are very mysterious. They are all integers. They have more than one digit. If you multiply them with ...Read More »
- Richie established a very strange number system. According to her claim for different combination of 0 and 2 you will ...Read More »