doesnt do the math correctly

```
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
scrs = sum(scores)
for score in scores:
variance += (average - score) ** 2
variance == variance / scrs
return variance
print grades_variance(grades)
```

help please

OUTPUT : 4342.92307692

None

Error : Oops, try again. grades_variance([7, 0, 2, 9, 7, 4, 8, 8, 2]) returned 85.5555555556 instead of the expected: 9.5061728395