number of cars in a train

例句：

1. 1.The number of students in the class is 30.
   班上的学生有30个。
2. 2.The number of cars in a train is 100.
   火车上汽车的数量是100个。
3. 3. The total number of people in the room is 50.
   房间里总共有50个人。