new_contents: from collections import Counter
  from matplotlib import pyplot as plt
  
  grades = [83, 95, 91, 87, 70, 0, 85, 82, 100, 67, 73, 77, 0]
  decile = lambda grade: grade // 10 * 10
  
  histogram = Counter(decile(grade) for grade in grades)
  
  left_scalars = [x for x in histogram.keys()]
  
  plt.bar(left_scalars, histogram.values(), 8)
  plt.axis([-5, 105, 0, 5])
  plt.xticks([10 * i for i in range(11)])
  plt.xlabel('Decile')
  plt.ylabel('# of Students')
  plt.title('Distribution of Exam 1 Grades')
  # plt.show()
  plt.savefig('grade_distribution_histogram.png', format='png')
  
subject: add histogram