Is there a grammar rule behind the hyphen in the phrase 'one-act play'?
Okay, so it might sound like a primitive question. However, I can find out a reasoning or maybe which form is correct.
The sentence is
This is a three parts series.
I'm not sure if I should add the delimiter or not; and maybe there is a possession "'s", and I'm not quite sure of that. So any help with explanation would be great!