text: grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
  
  def print_grades(grades):
      for grade in grades:
          print grade
  
  def grades_sum(grades):
      total = 0
      for grade in grades: 
          total += grade
      return total
      
  def grades_average(grades):
      sum_of_grades = grades_sum(grades)
      average = sum_of_grades / float(len(grades))
      return average
  
  def grades_variance(scores):
      average = grades_average(scores)
      variance = 0
      for score in scores:
          variance+=(average-score)**2
      result = variance/float(len(scores))
      return result
      print grades_variance(grades)
  
  def grades_std_deviation(variance):
      return variance ** 0.5
      variance = grades_variance(grades)
      print grades_std_deviation(variance)
  
  
  print print_grades(grades)
  print grades_sum(grades)
  print grades_average(grades)
  print grades_variance(grades)
  print grades_std_deviation(grades_variance(grades))
  