these nouns are singular, they take a singular verb; but because they denote a plural
idea, there is a strong tendency to use a plural verb instead, especially when a plural
noun is involved too:
La mayoría no estaba(n) de acuerdo.
The majority did not agree.
La mitad de los jóvenes no querían salir.
Half the young people did not want to go out.3.2.2.3 When haber is used in the sense of ‘there is’, ‘there are’, it is always singular, no matter
whether the noun that goes with it is singular or plural (you may sometimes hear a
plural used by speakers from some regions, but this is not regarded as grammatically
‘correct’):
Habrá muchos invitados. There will be many guests.
38.1 (p. 226)
3.2.2.4 Ser agrees with the noun that follows it rather than with its subject:
El problema son los otros.
The problem is other people.PLURALS AND NUMBER AGREEMENT 3.2