I'll try to answer your "50-year-old" question: You'll find that you describe a quality that has a quantity attached to it, you'll drop the 's'. The reason is

I'll try to answer your "50-year-old" question: You'll find that you describe a quality that has a quantity attached to it, you'll drop the 's'. The reason is mostly to keep things brief by omitting a verb. A few examples: - We walked a ten kilometer-long trail. (The trail we walked is ten kilometers long) - They are building a 500 seat auditorium. (The auditorium they are building has 500 seats.) - We'll put a 10,000 piece order in on Monday. (Compare to: the puzzle has 10,000 pieces.) Hyphenation is tricky and I still don't know all the rules. Another correction I'll make on > (merriam-webster agree with you) It should be "Merriam-Webster agrees with you" because in this case it refers to the dictionary itself (singular) and not the people the dictionary is named after. "Merriam and Webster agree with you" refers to the people themselves. It's occurring to me now that being a native English speaker is probably my best trait for hiring.