The number of ballot papers did not tally with the number of voters. Why here in this question article THE is not used before BALLOT PAPERS and VOTERS while we are talking about certain ballot papers and certain people who voted?
because they used an adjective of quantity "number of" before the noun "Ballot".
so the definite article "the" which placed at the beginning is so goes with the noun phrase " number of ballot"
"The number of ballot papers " is a noun phrase....'the' defines the noun "ballot papers"
so we couldn't put another "the" for the second time with the noun 'ballot papers'.
when we avoid the adjective "number of", the article "the" directly puts before the noun;
(The ballot papers.......) This sentence hasn't adjective which express the amount of the ballots.