There are fifty students in this class, three fifths of them are boys, so the number of the boys is 30.

这个班有50个学生，其中五分之三是男孩，所以男孩的人数是30。

youdao

The teacher has deleted from the name list the names of the students who haven't shown up in class three times in succession, and they will not get scores for this semester.

连续三次都没来上课的同学在名单中勾除，他们这学期就没有成绩了。

youdao

Actually three of our graduates or current students are teaching fellows in this class.

我们有三名毕业生或在读生,是这门课的助教。

哈佛公开课 - 幸福课课程节选