Let's analyze it with mathematical knowledge from a biological point of view. As we all know, it depends on whether the father's fertilized chromosome is Y type or X type. If it is Y type, it will give birth to a boy; If it is type X, it will give birth to a girl. However, the probability of male parents providing X type and Y type is the same, each accounting for 1/2.
From this point of view, whether the first child is a boy or a girl, how many boys or girls are born, the probability that the next child is a boy or a girl is 1/2.
So, what is the 2/3 answer? This brings us famous examples of boys and girls in statistics. The original question roughly means this. It is known that a family has two children, one of whom is a girl. Find the probability that the second child in this family is a boy.
First of all, since there are two children, and one of them is a girl, if the first condition is met, all the gender of the children in this family are: (female, female) (female, male) and (male, female).
Coupled with the second condition, in all the results of the first condition, only the second child (female, male) is a boy, accounting for 1/3 of all cases. So the final result is 1/3.
Based on the above two situations, I prefer the first result, namely 1/2. There are two main reasons.
The first reason is that statistics is the law of a large number of groups that react regularly, or the law reflected by the repeated occurrence of a situation. The topic involves a family and two children. In this case, many statistical laws can not be well reflected in individuals, and even the actual results will be contrary to the statistical laws. In other words, individual cases sometimes do not adapt to statistical laws.
The second reason is that we carefully compare the stem mentioned in the above calculation probability with the title of this article, and careful readers will find that it is different from the question in the title, that is, two different questions. Because the questions are different, the answers are often irrelevant.
The answer of 1/3 is so popular because the problem of having boys and girls is a widely used and famous case of conditional probability in statistics, and the theoretical basis of conditional probability is the famous Bayesian formula in statistics. You can search Bayesian formula by yourself, and many articles have detailed descriptions, so I won't go into details here.
It should be noted that with the progress of the times, the idea of "carrying on the family line" for boys and girls is not as serious as before, and some families even want to be "DINK" families. In addition, in contemporary social life, the "three cardinal guides and five permanents" in feudal thought has been weakened, and girls can do many things that boys can do, even better than boys. In addition, the phenomenon that the old people at home are left unattended due to the unfilial son occasionally occurs on the Internet. Many families have changed from "having a boy" to "having a girl".
Finally, it is fate to have boys and girls. Both boys and girls deserve the attention and care of every family.