Thanks man!!!
You're welcome!
But what about the word "people"? Isn't this also a collective noun?
Well, yes, and no; you just
had to pick that word, didn't you?
Check the definition and usage of
people. In part, the Usage Note says:
. . . Some grammarians have insisted that people is a collective noun that should not be used as a substitute for persons when referring to a specific number of individuals. By this thinking, it is correct to say Six persons were arrested, not Six people were arrested. But people has always been used in such contexts, and almost no one makes the distinction anymore. . . .
The most common usage is "how many people".
So, what makes the difference here?
Again, it's indefinite number versus indefinite quantity. See the first definition in the link above:
1. Humans considered as a group or in indefinite numbers: People were dancing in the street. I met all sorts of people.
To put it another way,
individuals or discrete "things" are measured in numbers (how many?),
"stuff" is measured in quantity (how much?).
How much sugar? (What
quantity of sugar?)
Two cups of sugar.
How many cups of sugar? (How many
units of measure of sugar?)
Two cups.
How many nails? (How many
individual nails?)
A dozen.
or [if you need a lot more.
]
Two pounds. (How
many units of measure of nails?)