input: from typing import List
  
  def calculate_mean(numbers: List[int]) -> float:
      """ Calculate the average of numbers stored in an array.
      >>> calculate_mean([10, 20, 30])
      20.0
      >>> calculate_mean([5, 15, 25])
      15.0
      """
output:     total = sum(numbers)
      count = len(numbers)
      return total / count