COLLECTIVE NOUNS AS SINGULAR OR PLURAL

Collective nouns, or collectives (family, team, couple, etc.), tend to be plural when the component members are considered separately and singular when the group is handled as a unit:

            a score were present

            an army marches on its stomach

The plural often prevails when humans are concerned:

            The couple are. . . .

The decision between singular and plural is frequently writer's choice.   Once the number is established, be consistent:

            My family trusts only people it knows

            my family trust only people they know

            Smith's team works long hours in the hot sun,

                        but it [not they] always maintains an esprit de corps.

             Piersma's team works fast; the scientists [not they] prepare

                        a net to be fired by mortars

            The enemy wasn't interested merely in conquest; it [not they] wanted

                        to wipe Aguateca off the map.

Generally speaking, a number, a fraction, or a quantity of things is singular if considered as a mass (10 gallons is enough) and plural if considered as separate units (10 dishfuls were slowly doled out).

Generally use a plural verb when human beings are implied:

            Half the wine is enjoyed ...

            Half of these people are engaged ...

            35 percent of the bread goes ...

            35 percent of the grapes go ...