...January the ninth.

1月9日

...students in the ninth grade.

9年级学生

...ninth century illustrated manuscripts.

9世纪配有插图的手稿

In Brussels the dollar rose by a ninth of a cent.

在布鲁塞尔美元升值了1/9美分。

What you see is only the tip. Eight ninths of it is under the sea.

你看到的只是一角，8/9的部分在海里。