X of Y
X: %, percent, number, fraction etc.
Y: subject
is a case where the combined subject is singular or plural, based on whether Y is singular or plural.
So,
A high
percentage of the population _____
is____ voting for the new school.
A high
percentage of the people ____
were_____ voting for the new school.
are the correct answers as
population is a singular and
people is a plural subject.
Some more examples:
10% of the students are not in the class (plural)
One third of the cake has been eaten (singular)
One more note:
The following words can result in
either a singular or plural subject based on the subject it acts on
1)
Some of :
Example:
Some of the cookies are missing - OK
Some of the cake is missing - OK
2)
Any of
3)
Most of
4)
All of
Hope this helps.