I always see the usage of "plurals are a singular", such as in Telegraph and Economist (below). What kind of grammer or usage is it? Under what circumstance I can use this "plurals are a singular"? Or I should avoid using it during some public examination as markers tend to deduct points on such usage?
Equities are 'preferred asset class' in 2010
Are persistent trade deficits a bad thing?
Anthony the student