The subheading above, in The New Paper (20 August 2010), contains a subject–verb agreement error. Since the subject is the noun phrase frequency of cases, whose head is the singular noun frequency, the following verb should be singular prompts and not plural prompt.
It is worth remembering that, even though we call it ‘subject–verb agreement’, the agreement is between the verb and the head of the subject noun phrase (if it is complex), and not with the noun nearest to it (so the verb doesn’t agree with cases).
A similar problem is seen here (same newspaper, same day). The subject is the non-finite clause locating the best places ... for effective exposure. Like all non-finite clauses functioning as subjects, it should be treated as singular, hence ... is all in a day’s work.