16. Exam Statistics

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 / len(scores)
    return result
    
print grades_variance
 
def grades_std_deviation(variance):
    return variance **0.5
 
variance = grades_variance(grades)
 
print grades_std_deviation(variance)