"The twenties was/were a carefree time."
I say it's was because twenties is acting as a singular era. A friend of mine says it's were because numbered year groups are plural, and only things like "the middle ages" is singular.
"A number of themes presented in The Great Gatsby require/requires an understanding of the time to appreciate fully the novel."
I think it would be requires because the subject is number. My friend says it should be require because, even though number is singular, you're talking about one thing. I brought up that what I was talking about in the sentence is in a prepositional phrase, so it doesn't matter. She gave this example: "Those trikes are cool. A bunch of them are blue, but a good number are red." The example makes sense to me, but I don't know if bunch and number are acting as predicate nominatives or something that may change the verb. (I don't know if that would change it, but I'm just trying to figure out why).
A. Good questions. I checked my handy Gregg Reference Manual to make sure of the answers.
1. Use a singular verb when periods of time represent a total amount. The book gives this example: Three months is too long to wait.
2. "The number" is singular, but "a number" is plural. Here is their example:
A number of our branches are now located in suburban malls.
3. "A bunch of them are blue..." In this sentence, "bunch" is a collective noun. Collective nouns can be singular or plural. In this sentence the members of the groups are acting separately, having different colors, so the plural verb is appropriate.