Learn Russian: Ряд демографических проблем требовал быстрого решения. - A number of demographic problems required a quick solution.

Even though the phrase translates to 'a number of problems', the grammatical subject here is the quantifier ряд, which is a masculine singular noun. When a quantifier like ряд or большинство is followed by an inanimate noun (like 'problems'), Russian strongly prefers strict grammatical agreement, so the verb matches the singular noun ряд. Plural agreement would be more common if the noun were animate, like a group of people.

Could we use a neuter singular verb here, like we often do with большинство?

No, you cannot use the neuter требовало here. Words like большинство (majority) or меньшинство (minority) are grammatically neuter, so they take a neuter singular verb. However, ряд is grammatically masculine. When choosing singular agreement for it, the verb must be masculine (требовал).

Why is the direct object быстрого решения in the genitive case rather than the accusative?

The verb требовать (to demand or require) can take either an accusative or a genitive object. At the B2 level, a good rule of thumb is that when you require something abstract or intangible—like a 'solution'—the genitive case (быстрого решения) is heavily preferred. The accusative is mostly used when demanding specific, concrete physical objects.

How does the word ряд function as a quantifier here?