text: #!/usr/bin/env python
  
  """Answer for 11.9 in chapter 11."""
  
  
  def average(a_list):
      """Caculate the average of a list."""
      return reduce(lambda x, y: float(x) + float(y), a_list, 0) / len(a_list)
  
  print average([1, 3, 5])
  print average([1, '2', 5])
  