为什么a great many people 这种说法是对的 a great many of the people也是对

A great many people意思就是说：很多人.
A great many of the people意思是：这些人之中的很多个
A great many其实你可以用many代替啊.这样句子就变成,many people 和many of the people.
Many people很显然就是“很多人”的意思.而many of the people就是“这些人之中的很多个人”
Many people are workers.很多人是工人.
Many of the people are workers.这些人之中的很多个都是工人.
就是这点不同.