How do you determine whether "Teller" is singular or plural in a sentence?
I don't think the article is ever dropped for (countable) singular nouns. That just doesn't sound right.
Try it in English: "the restaurants have plate". Doesn't work, right?
I hadn't considered that; you're right. I guess there are always two indicators of plurality: the word change and the article.
If it has an article, see if it has a masculine or plural pronoun (usu. "der" vs "die"). If it doesn't have an article, use context (in the same way as "sheep" in English).
Das Restaurant is singular and Die Restaurants is plural(all plurals are with die)
Then why do they need to borrow ours?!
(referring to another comment trail)