my @chapters          = ( 15, 24, 23, 110, 30, 58, 3, 22, 79, 6 );
my $chapter = 1;
my @sentenceToChapter = (
    undef, # start counting at 1
    map { ($chapter++) x $_ } @chapters,
);

print qq{Sentence $_ is in chapter $sentenceToChapter[ $_ ]\n}
   for qw{ 250 15 16 98 };