input: 
  from typing import List
  
  def calculate_rRNA_percent(gtf_file: str, htseq_counts_file: str) -> float:
      """ Calculate the percentage of transcripts mapping to rRNA from the given HTseq count file and GTF file.
      >>> calculate_rRNA_percent('/path/to/GTF/file', '/path/to/HTseq_counts/file')
      3.25  # Example output, actual value will vary based on input files
      """
  
output:     rRNA_counts = 0
      total_counts = 0
  
      # Read GTF file to identify rRNA features
      with open(gtf_file, 'r') as gtf:
          for line in gtf:
              if 'rRNA' in line:
                  rRNA_counts += 1
  
      # Read HTseq counts file to get total counts
      with open(htseq_counts_file, 'r') as htseq:
          for line in htseq:
              total_counts += 1
  
      # Calculate percentage of rRNA counts
      rRNA_percent = (rRNA_counts / total_counts) * 100
  
      return rRNA_percent