verb agreement - "5 votes {was/were} chosen to be the number of close votes needed...": Which is correct?

"5 votes was chosen to be the number of close votes needed to close a question"

Grammarly says that I should change "was" to "were," but it doesn't sound right to me. What's the correct conjugation to use here, singular or plural?

Answer

To paraphrase your sentence, you would say:

The number of close votes needed was five.

The subject of the sentence is the number (singular) so the verb takes a singular form.

(Or, more precisely, it's the entire subject phrase the number of close votes needed, because the number is modified by of close votes needed. But for the sake of this explanation, it's easiest to think of just the number.)

Just as you would say:

The number is five.
The numbers were five and six.

Again, the verb matches the singular or plural subjects.

So, going back to the actual phrasing of your sentence:

5 was chosen to be the number of close votes needed.

The subject remains the number and the verb remains in the singular.

Note: As per a perfectly correct comment, the number of votes cannot be 5 votes; it is simply 5. I have edited the actual sentence to correct this.

The sentence in question has been constructed in such a way that 5 votes misleads you into thinking that it's the subject.