表具体时无复数，不加s
基数词+hundred(百)/thousand(千)/million(百万)/billion(十亿)
例：three hundred people 三百个人<br>three hundred and one 三百零一
复合形容词：a/an 基数词+连字符+名词
例：a ten-minute walk = ten minutes' walk
表年龄
某人...岁：基数词+years old
例：He is twenty years old = a twenty-year-old man
在某人...岁时：at the age of +基数词
例：He is at the age of twenty
在某人n十岁时：in one's+ 整10基数词的复数形式
例：Tom published a novel in his/Tom's twenties <br>汤姆在他二十多岁的时候出版了一部小说
表倍数
一倍(次)：once
两倍(次)：twice
三倍(次)及以上：基数词+times
例：I have been to Beijing three times
