How many cars?

1 in 4 cars is short of oil. (From an oil company advertisement.)

Doesn’t this strike you, on first reading, as ungrammatical? It’s the close combination of ‘cars’ and ‘is’ that causes the problem, because, strictly speaking, it’s correct. But to the ear there’s an awkwardness which no amount of repeating will make come quite right. Far better for the copywriter to have written: 1 car in 4 is short of oil. The change makes all the difference to our innate sense of grammar.