The number of male students is 2 / 3 of that of female students, and what is the number of male students in the class? Why?

The number of male students is 2 / 3 of that of female students, and what is the number of male students in the class? Why?

Boys are 2 / 3 of girls, that is to say, there are 2 boys and 3 girls
2/(2+3)=2/5