One in five of us is (are?) confused by this
A recent set of posts on the American Copy Editors Society discussion board debated correct grammar with expressions like "one in five of those polled say (or says?) ..."
The grammar books mandate the singular, but a growing and influential group of people says (say?) what is more important is the sense of what is meant -- in this case that one in five really represents a larger concept.
What to do when grammar doesn't let me say what concept I meant? A corner of grammar called notional agreement or synesis deals with this, and editors can't afford to dismiss how such concepts are changing our language and usage. Read all about it in this month's Common Sense Journalism column.