15 + plural noun
作定语修饰复数可数名词，表示数量“十五”。
There are 15 students in the classroom.
教室里有15名学生。
十四加一的基数
the number fifteen
十四加一的基数
the cardinal number that is the sum of fourteen and one
15 is between 14 and 16 on the number line.
15在数轴上位于14和16之间。
用法提示：此处“15”作主语名词，表示基数十五。
He counted to 15 in English during the game.
游戏时他用英语数到了15。
用法提示：此处“15”作介词宾语，指数数时到达的基数十五。
If you double 15, the result is 30.
如果你把15加倍，结果就是30。
用法提示：此处“15”作动词“double”的宾语，表示作为基数的十五。
作定语修饰复数可数名词，表示数量“十五”。
There are 15 students in the classroom.
教室里有15名学生。
表示年龄，口语中也常简说 at 15。
He left home at the age of 15.
他十五岁时离开了家。
percent 后接 of 再加名词；谓语动词的单复数取决于 of 后面的名词。
15 percent of the students passed the exam.
百分之十五的学生通过了考试。
“in + 时间段”表示将来“在……之后”，不要与表示时长的 for 混淆。
The train leaves in 15 minutes.
火车十五分钟后出发。
grammar · medium
易错句子There are fiveteen students in my class.
正确表达There are fifteen students in my class.
英语里 15 拼作 fifteen，不是在 five 后面直接加 -teen：five 在 -teen 前要变成 fif-（同理 fifty），所以 fiveteen 是错误拼写。
grammar · medium
易错句子She has a fifteen-years-old son.
正确表达She has a fifteen-year-old son.
数词加名词作定语修饰另一个名词时，要加连字符并把名词改为单数，即 fifteen-year-old；-s 只出现在作表语的句型 “He is fifteen years old” 中。
fifty 表示“五十”，15 表示“十五”；两者拼写和发音相近，但重音与结尾不同，数值也不同。要表达数量 15 时用 15/fifteen，表达 50 时用 fifty。
adj.
adv./adj.
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