```
grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
#grades = [1, 4, 2, 3, 5, 7, 3, 8, 4]
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(grades)
variance = 0
for score in scores:
variance += (average - score) ** 2
return variance
def grades_std_deviation(variance):
return variance ** 0.5
variance = grades_variance(grades)
#print grades_std_deviation(variance)
print grades_sum(grades)
print grades_average(grades)
print grades_variance(grades)
print grades_std_deviation(variance)
```

the error i get is this :

Oops, try again. grades_variance([47, 6, 49, 50, 92, 68, 35]) returned

10920.4837278106instead of the correct value608.2448979592

EDIT: everytime i execute this exercise i get a different answer. for example :

grades_variance([74, 53, 21, 51, 7, 37, 51, 16, 37]) returned

19368.2263313609instead of the correct value399.1358024691

BUT, it prints this

1045.5

80.4230769231

4342.92307692

65.9008579377

None

Thanks for the help in advance.