thirty

三十的、三十個

Thirty people signed up for the beginners' cooking class.

有三十個人報名了初級烹飪課。

三十

Thirty is the number he always picks in the lottery.

三十是他買彩券時固定會選的號碼。

三十歲、三十幾歲常用複數

She went back to school in her early thirties.

她三十出頭時重返校園讀書。

三○年代常用複數

The film is set in the thirties, just before the war.

這部電影的背景是三○年代，就在戰爭爆發前。