input: def calculate_average(numbers: List[float]) -> float:
      """ Calculate the average of a list of numbers.
      >>> calculate_average([1.0, 2.0, 3.0, 4.0, 5.0])
      3.0
      >>> calculate_average([10.5, 20.5, 30.5])
      20.5
      """
output:     return sum(numbers) / len(numbers)