number of terms in a series

例句：

1. 1. The numberof students in the class is 30.
   班级里的学生有30个。
2. 2.The total number of items sold was500.
   总共卖出了500件商品。
3. 3. The number of stars onthe moon is a mystery.
   月球上的星星数量是一个谜。