input: from typing import List
  
  def calculate_mean(numbers: List[float]) -> float:
      """ Calculate the average of numbers in the given list.
      >>> calculate_mean([10, 20, 30])
      20.0
      >>> calculate_mean([12.5, 15.5, 18.5])
      15.5
      """
output:     total = sum(numbers)
      count = len(numbers)
      return total / count