A 'percentage' is a ratio that is compared to 100.

You are creating a ratio that is based on 1, not 100.

my $ratio_correct   = $number_correct / $total_number;
my $percent_correct = $number_correct * 100 / $total_number;
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It may also be that you're confused by what '%.2f' does in the context of (s)printf ... From perldoc for sprintf:

  .number "precision": digits after decimal point for
          floating-point, max length for string, minimum length
          for integer
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If you're trying to truncate in perl, I'd recommend using '%d', not '%.f' or '%.0f', so it won't round up.