percentage

If you put the definite article the before percentage, you are stipulating just one percentage and thus you must use a singular verb: The percentage of errors in this term paper is large. If you put the indefinite article a before percentage, use a plural verb when the noun or pronoun in any subsequent prepositional phrase is regarded as a countable plural, not a unit or a whole: A large percentage of the errors are found in this text. If the noun or pronoun object in such a phrase is singular or is regarded as a unit or a whole, use a singular verb: A large percentage of the electorate remains undecided.

Do not use a percentage of (or a proportion of) when you mean "some," as in A percentage of the students have laptop computers. The words percentage and proportion are meaningless unless qualified by an adjective such as large or small, as in a large proportion of the work, and they are still best avoided where many, much, a few, or a little can be used instead.