I'm having problems with hundred and thousand.
If someone asks you, How many trees are in this forest? Would you answer seven thousand or seven thousands, because thousands are countable?
I know that you usually say seven thousand, but I also know that thousands are countable, so wouldn't that make it seven thousands?
And when you are talking about multiple countable nouns, you would make it plural, but the plural isn't thousand, it's thousands, so it couldn't be that thousand is the plural.
Why isn't it a few thousands? Is it because of an exception in English? Any help would be appreciated.