He took the examination after six months. Then another. And another.

六个月后，他通过一门考试。之后又是一门。然后还有一门。

Fifty percent of the students who took the examination scored above 450.

50%的学生考试成绩都在 450 分以上。

An " administration" of an exam is an opportunity to take the examination – to take the test.

一次“考试” 是一次参加考试的机会——参加考试。