how many students in your school?
=what's the number of the students in your school?
你们学校的人数是多少?
the number of 与a number of 的区别:
The number of +可数名词+单数动词(动词必须为单数,因为number作主语,是不可数名词)
表示".数量,数额."
例:
The number of homeless people has increased two thousand.
无家可归者已经上升到2000人了.
a (large,small) number of +可数名词+复数动词(动词必须为复数,因为是可数名词做主语)
例:
A large of people have lost their lives in earthquake.
很多人做地震中遇难.