Generally, the first child will give birth to a boy and a girl every four years.

After four years, all the children are male or female. I believe that none of us are fortune tellers.

The key lies in the man's chromosome and the "luck" between husband and wife.

Believe in science, if you guess that the ratio of male students to female students is 50%, wouldn't it be in vain?

I hope my answer will make you feel something.