One in five don't care [duplicate]

Solution 1:

Both are commonly used and acceptable.

There are various common cases where a superficially singular subject can or indeed must be associated with a plural verb:

The government [are/is] considering the proposal.

A lot of these matters [have/*has] been dealt with.

The majority [are/??is] pleased with the outcome.

A half of all pensioners [are/??is] living below the poverty line.

In the case you mention, a plural verb is probably at least equally common nowadays as a singular, though historically a singular verb appears to have been more common (e.g. do some comparisons on Google NGram: the singular verb appears to have undergone a downward trend over the last couple of centuries).

You will find prescriptivists bemoaning the apparent contradiction of a singular noun accompanied by a plural verb. But there's really no God-given reason to expect the verb to agree necessarily with the head noun and actual data clearly contradicts this assumption. As is usually the case, the prescriptivists are inventing a problem because their grammatical model is inadequate.

Solution 2:

In data analyzed for the ‘Longman Grammar of Spoken and Written English’ on constructions with one in or one out of followed by a number, plural agreement predominated. ‘The Cambridge Grammar of English Usage’, which quotes this finding, comments that ‘For most writers the choice depends on whether you’re thinking of a single case or a general principle.’

Solution 3:

"One in ten children" may be a fraction, but you are still talking about one child, even as a generality. Out of group of ten children at random, you are considering just one. The singular is/has is appropriate.

If you were to say "10% of children"or "a tenth of all children", then you are talking about a general group of children and the plural are/have is appropriate.

Solution 4:

I think an alternative is:

One child in ten is dyslexic.

versus

One child in ten are dyslexic.

which seems to be incorrect. This puts the emphasis on the fact that there is one child, which is singular, that makes the verb be is rather than are.