One in ten is or are?

Which is the correct verb in the sentence below?

(1) One in ten respondents was/were unhappy with the new rules.

Sometimes the noun is understood and omitted:

(2) One in ten was/were unhappy with the new rules.

Well, it's never an easy answer as both the singular verb and the plural verb have been used in written texts.

Grammatically, the subject of one in Number is one, which is singular and therefore requires a singular verb:

(3) One in ten respondents was unhappy with the new rules.

In formal contexts, the singular verb is less likely to be met with objection.

But, notionally, as others argue, the phrase one in ten respondents refers to not one but some number (of respondents), and therefore requires a plural verb:

(4) One in ten respondents were unhappy with the new rules.

For instance, if there are 500 respondents, one in ten respondents means 50 respondents, a plural sense. This argument is particularly appealing if we use a pronoun test:

(5) One in ten respondents say they do not like the movie.

Sentence (5) uses the plural verb say and the plural pronoun they, both of which (notionally) agree with the plural sense of One in ten respondents.

Contrast (5) with (6) and (7) below:

(6) One in ten respondents says they do not like the movie.
(7) One in ten respondents says he does not like the movie.

In (6), the singular verb says agrees with One but their use is inconsistent with the plural pronoun they.

In (7), the singular says agrees with One but the singular pronoun he is potentially ambiguous as it can be interpreted as referring to someone else other than the head noun One.

That leaves us with sentence (5), which does not suffer from the grammatical inconsistency of (6) and the potential pronoun ambiguity of (7).

So, does that mean we should use the plural verb?

Well, not exactly. As we have hinted at the beginning, there is no clear-cut answer. In formal English, the singular interpretation and hence the singular verb are preferred. The plural verb, while notionally sound, goes against grammar rules and one must be prepared to defend its use.